L -12758-TThesis

UC-714Issued:April1994

Conceptual Design ofa Digital Control Systemfor Nuclear Criticality Experiments

St@zen PaulRojas*

“GraduateResearchAssistantat Los AlamosGroupNE-6.

Los Alamos, New Mexico 87545

ACKNOWLEDGMENTS

The authcr gratefullyacknowledgesall staffand personnelof the AdvancedNuclear

Technologygroup,NIS-5,at Los AlamosNationalLaboratoryfor their guidance,

support,and assistancein completingthis study.

v

TABLE OF CONTENTS

List of Tables...

00,.....0... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . lull

List ofAppendix Tables..................................................................................xiv

List ofFigures ................................................................................................xv

List ofAbbreviations.......................................................................................xvii

Chapter

1. INTRODUCTION.....................................................................................1

l.l Background. .. . . . . . . . -.--.~---~--~.~~-~~-~~-~- ..-.....................1

l.l.l NuclearCriticality.......................................................................1

1.1.2MultiplicationFactor..-------ti--.--.-.-------- ....................1

1.1.3 FissileMaterial.. . . . . . ------------------------ ...............2

1.1.4PromptandDe1ayedNeutrons....................................................3

1.1.5 Cross Sections. . . . . . -...-----.--------..-.. ...................3

1.1.6Moderatorsand Poisons.............................................................3

1.1.70ver/UnderA40deratedSystems.................................................4

1.I.8PromptandDelayedCriticality ...................................................4

1.1.9ReactiviQ----------- ------------------------ ................5

l.l.lOAtom andNumberDensities......................................................5

l.l.ll ScramSystem............................................................................6

1.1.12HistoricalPerspective:LACEF.................................................6

1.20bjeetives ............................................................................................8

1.2.1MechanicalSystem......................................................................9

1.2.2HydraulicSystem.........................................................................10

1.2.2.1 Valves.................................................................................. 11

1.2.2.2Accumulator........................................................................ 11

1.2.2.3PressureSwitches................................................................ 11

vii

1.2.2.4Pump...................................................................................11

1.3Scope ofStudy ....................................................................................12

1.4ReportOutline ....................................................... .............................12

2.THE NUMERICALSTUDY.....................................................................13

2.1 Introduction.........................................................................................13

2.2 The Monte CM1OMethod....................................................................13

2.3 Los AiamosNationalLaboratoryand MonteCmlo........ . . . . . . .15

2.41nput File Overview..............................................................................16

2.5 UranylNitrateSolutionSystem...........................................................18

2.6 Results.................................................................................................21

2.7Summary .............................................................................................24

3. CONCEPTUALMECHANICALDESIGN..............................................25

3.1 Basic MechanicalRequirements..........................................................25

3.2 options for Performingthe SlabTanks Experimenton Honeycomb... . . . . . . . . . . . . . . . . . . . . . . . . . .26

3.3 MechanicalDesign Concepts. ...............................................................28

4. APPROACHESTO CRITICALEXPERIMENTCONTROL.............,....30

4.1 GeneraIModeofOperation .................................................................30

4~DigkalVs.An~ogHtitititio um.~.mm..~~..t~~ti~~~~ti~~. .................31

4.3 Custom Digita!Systems......................................................................31

4.4 PurchasedSystems..............................................................................32

5. CURRENTCONTROLSYSTEMHARDWARE....................................,33

5.i Introduction............................................................. ............................33

5.2Test Bench ControlSystem..................................................................35

5.3 Configuringthe System........................................................................37

5.4ComponentSumm~ ...........................................................................37

...Vlll

5.4.11785 PLC-5115Processor...................e.......................................37

5.4.21771-IBD DC inputModule... . . . . . . . . . . . . . . . . . . . . . . ........38

5.4.31771-OBD DC OutputModule. . . . . . . . . . . . . . . . . . . . . . . . . ..38

5.4.41771-IFEA AntdogInputModule.-.. -------- ........................38

j.4n5120VACPowerSupply ....~.......~~~..ti....... ..................38

5.4.6 CompumotorA.YLDrive..............................................................39

5.5 Control of DC Stepper Motors. . . . . . . . . . . . . . . . . . . . . . . ..............39

5.6 The StepperMotorDrive:Characteristicsand Selection......................41

6. CONTROLSYSTEMEXPANSION.........................................................43

6.1 PLCSystem ExpansionInto Kva I---------------- ....................43

6.1.11771-ASBRemotel/O Adapter. . . . . . . . . . . . . . . . . . . . . . . ......44

6.1.21771-MI StepperControlModule...............................................44

6.1.31771-OJPulse OutputExpander.. . . . . . . . . . ............................44

6.2 Control ofACSynchrcmous ConstantSpeed Motom..........................45

7. USING THE NUMERICALRESULTSTO SIZE HARDWARE...........48

7.1 Introduction. . . . . . . . . . ---.--ti.n...------~-.~- ...................-...48

7.2 HorizontalSolutionAssembly:the SlabTmks..... . . . . . . . . ..........48

7.2.1Requirements...............................................................................48

7.2.2A4aximumSpeedAllowable... . . . . . . . . . . . . . . . . . . . . . . . . ......50

7.2.3BasicFormulas. . . . . ----------------------- ...................51

7.2.4MaximumPulseRate... . . . . .. . . .. . .. . . . . . . . . .. . ...................52

7.2.5h4inimumSpeedPossible... . . . . . . . . . . . . . . . . . . . . . . . ...........52

7.2.6Resolution....................................................................................52

7.2.7RequiredOperating Torque........................................................53

7.2.8GearheadReduction....................................................................54

ix

7.3 Summary.................................................................,...........................55

8. CONTROL SYSTEM PROGRAMMING...............,................................57

8.1 Introduction.........................................................................................57

8.2 Basic ProgrammingConcepts. . . . . . . . . . . . . . . . . . . . . . . . . ............59

8.3 Programmingthe Ana!ogInput Module..............................................59

8.4 Programingthe StepperMotor Modules.............................................60

8.5 Programmingan IntegratedDrive........................................................60

8.6 StepperControlVia an IntegratedDrive..............................................61

8.7 SequentialFunctionChart: File 001.....................................................63

8.8 Ladder ‘Logic:Files 002-12..................................................................65

8.8.1 Rung2:0--ti --------- ------------------------- ............65

8.8.2 Rung2:1......................................................................................65

8.8.3 Rung2:2......................................................................................65

8.8.4 Rung2:3......................................................................................66

8.8.5 Rung3:0......................................................................................66

8.8.6 Rung4:0......................................................................................66

8.8.7 Rung4:1......................................................................................66

8.8.8Rungs4:2 ....................................................................................67

8.8.9 Rung4:3......................................................................................67

8.8.10 Rungs4:4-4:8.............................................................................67

8.8.11 Rungs4:9-4:10..........................................................................67

8.8.12 Rung6:0....................................................................................67

8.8.13Rungs 7:0..................................................................................67

8.8.14 Rung8:0....................................................................................68

8.8.15 Rung9:0....................................................................................68

3.8.16 Rung10:0..................................................................................68

x

8.8.17Rung10:1..................................................................................68

8.8.18Rung10:2..................................................................................68

8.8.19 Rung10:3...................................................................................69

8.8.20 Rung10:4...................................................................................69

8.8.21Rung10:5...................................................................................69

8.8.22Rung11:0....,.............................................................................69

8.8.23Rung11:1..................................................................................69

8.9 summary.............................................................................................70

9. USER INTERFACESOFI’WARE............................................................71

9.1 Ovexview..............................................................................................71

9.2 GeneralFeatures..................................................................................71

9.3 UranylNitrateExperimentinterface....................................................72

10.COST ESTIMATE...................................................................................75

!0.1 Labor Cos(s.......................................................................................75

10.2MaterialCosts....................................................................................75

10.2.1MechanicalHardware...............................................................75

10.2.2ControiS).slem Hardware .........................................................76

10.3cost summary ...................................................................................77

11. CONCLUSIONS ~ 78.....................................................................................

REFERENCES...............................................................................................80

APPENDICES...............................................................................................83

A. MCNP CARD SUMMARY....................................................................83

B. NUMBERDENSITY CALCULATIONS..............................................89

C. CONTROLPROGRAM LISTING....................................................... %

D. INPUT FILES........................................................................................ 117

xi

E. NUMBER DENSITYTABLES.............................................................. 125

xii

LIST OF TABLES

Table 2-1: AssumedValues for Number DensityCalculations.....................19

Table 2-2: Mdel Materials . . . . . . . . . . . . ....ti.............--....20

Table 3-l: MechanicalFunctionand SolutionFrom MosttoLeast Essential.............................................................................28

Table 6-1: Control ComponentsforKIVA IonHand .................................44

Table 6-2: NecessaryControl SystemComponentsfol KJVA.....................44

Table 7-1: MechanicalRequirements...........................................................49

Table 7-2: Load Requirements.....................................................................49

Table 7-3: SizingCalculationsSummary.....................................................56

Table 8-1: S]abTank ProgramFiles. . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...63

Table 10-1: ApproximateHardwareCosts ...................................................76

Table10-2: ApproximateControlHardwareCosts......................................’76

Table 10-3: TotalEstimatedCost .................................................................77

...Xlll

LIST OF APPENDIXTABLES

Table E-1: Number Densities.......................................................................127

Table E-2: .4tomFractions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .....128

xiv

LIST OF FIGURES

Figure l-l: CriticalityWindow...........,,, , .0,..,... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Figure 1-2: PajaritoSite (TA.l8)..................................................................8

Figure l-3: SystemsOverview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..9

Figure l-4: HydraulicSystem...................................................... ...............10

Figure 2-1: ADart GameWith a HypotheticalFrequency13istribution.......l4

Figure 2-2: FissionCross Sections for SelectedIsotoPs ....-.-...-..-l7

Figure 2-3: Slab Geomet~........ ...................................................................19

Figure 24: &ff Vs. Air Gap ......................................................................2l

Figure 2-5: ReactivityVs.AirGap . . . . . . . .......--.-..............22

Figure 3-1: CurrentExperimentalConfiguration(“Honeycomb’’)..........,.....26

Figure3-2: AdjustmentsIdeallyAvailablefor SlabTank Alignment(S!abTank on MovableCart) 77......................................................A-

Figure 3-3: MicrometerAdjustmentwith aLead ScrewConcept..................28

Figure 3-4: An Option for the Mechmic~Configuration...........-...29

Figure4-1: Block DiagramoftheGeneral Control System. . . . . . . ............30

Figure5-1: TypicalCriticalAssemblyControlDeviceRequirements...........33

Figtire 5-2: CurrentControlRoomOne Configuration................................34

Figure 5-3: Programand HardwareTest Station.... ......-..........35

Figure5-4: Control HardwareatPajarito......................................................36

Figure 5-5: DC StepperControl Options.....................................................40

Figure 6-1: AnticipatedKIVAI ControlSystem..........................................43

Figure 6-2: AC Motor ControlCircuti. . . . . . . . . . . . . . . . . . . ....................46

Figure 7-1: StepperMotorVelocityProfile..........................50

Figure 8-1: Signal FlowThrough the System...............................................58

Figure 8-2: 13asicPLCProgramming Concepts......................59

xv

Figure 8-3: Analog InputProgramming.......................................................60

Figure 8-4: General Featuresof the SFC......................................................64

Figure 9-1: Screen Shot of ComputerGeneratedControlDisplay...............74

xvi

LK)TOFABM.EVIATIONS

PLC: ProgrammableLogicController

SCRAM:quickdecreaseinsystemreactivityduetotheengagementofmechanical

motiondevices

PROM: ProgrammableRead Only Memory

PID: ProportionalIntegralDerivative

IT”L:TransistorTransistorLogic

AIX: Analogto DigitalConvefier

MCNP: Monte Carlo NeutronPhoton Code

LACEF:Los AlamosCriticalExperimentsFacility

DOE: Departmentof Energy

NEMA:NationalElectricalManufacturersAssociation

SHEBA: SolutionHigh EnergyBurst Assembly

RAP: RemoteAutorangingPiccometer

SST: StainlessSteeI

BCD: BinaryCoded Decimal

xvii

CONCEPTUALDESIGNOFADIGITALCONTROLSYSTEMFOR

NUCLEAR CRITICALITY EXPERIMENTS

by

Stephen Paul Rojas

ABSTRACT

Nuclearcriticalityis a concernin manyareasof nuclearengineeringincludingwastemanagement,nuclearweaponstestinganddesign,basicnuclearresearch,and nuclearreactordesignand analysis. As in manyareasof scienceand engineering, experimentalworkconductedin this fieldhasprovideda wealthof data and insightessentialto the fommlationof theoryand the advancementin knowledgeof fissioningsystems.In light of themanydiverseapplicationsof nuclearcriticality,thereis a continuinginterestto learn and understandmore about the fundamentalphysicalprocessest’hroughcontinuedexperimentation.This thesisaddressesthe problemofsettingup and programminga microprocessor-baseddigitalcontrol system(PLC)for a proposedcriticalexperimentusing.amongotherdevices, asteppermotor,a joystickcontro!mechanism,and switches. Thisexperimentrepresentsa revisedconfigurationto testcylindricalnuclearwastepackages.

A MonteCarlo numericalstudy for the proposedcriticalassemblyhasbeen performedin order to illustratehow resultsfrom numericalcalculationsare used in the processof assemblingthe control systemand tocorrobor : previousexperimentaldata.This studyinvolvesmodelingasolutionsystemof uranylnitratein cylindricalgeometry(twocylindrical“slab”tanks approximately28 inchesin diameterand 4 inchesthick) withthe MonteCarloNeutronPhotoncode writtenat Los AlamosNationalLaboratory,New Mexico.The resultsof this studyyieldedthe sensitivityeffect of varyingthe distancebetweenthe tanks:informationused as designcriteriato size variouscontrolsystemcomponents.In addition,the softwarenecessaxyfor experimentcontrolwas developed.

In summary,a controlsystemutilizingsomecommondevicesnecessaryto performa criticalexperiment(steppermotor,push-buttons,etc.) has beenassembled. Controlcomponentswere sized usingthe resultsof aprobabilisticcomputercode (MCNP).Finally,a programwas writtenthatillustratesthe couplingbetweenthe hardwareand the devicesbeingcontrolledin the newtest fixture.

xix

Chapter 1.

INTRODUCTION

1.1 Background

1.1.1 NuclearCriticality

The term “criticality”gerlerallyrefers to the studyof fissioningsystems that

approacha state of equilibriumbetweenthe numberof neutronsbeing producedand

the number of neutrons “dying.”Neutrons are producedby the process of nuclear

fission. In a Los AlamosNationalLaboratoryreport [15], Hugh C. Paxton defines the

fissionprocess as:

The disintegrationof a nucleus (usually,Th, IJ, Pu, or heavier) into twomassesof similarorderof magnitude,accompaniedby a ‘argerelease of energyand the emissionof neutrons. Althoughsome fissionstake place spontaneously,neutron-inducedfissionsare of major interest in criticalitysafety....

Thus, the area of major interest in nuclearcriticality is in the generationand death of

neutrons. The same diffusiontheory that has successfullybeen applied to heat transfer

and fluid mechanicshas also been successfullyused to model the process of nuclear

fission. In addition,as will be seen in chapter thee of this document,probabilistic

approacheshave provenextremelyusefulin the designand analysisof f~sioning

systems.

1.1.2MultiplicationFactor

The multiplicationfactor is denotedwith the symbol “k”and is defined as

follows [9]:

k=numberoffissions in current generation

numberoffissions inpreceding generation

So if the multiplicationfactor is less than one, then the system is called “subcritical”

and the numberof fissionsoccurringin the system is decreasingwith time. On the

other hand, if the multiplicationfactor is greater than one, then the sys:cm is said to be

“supercritical”and the numberoffissionsincreaseswithtime. Ifthemi!hiplication

factor is equal to one, then the system is said to be exactly “critical”ar:dthe number of

fissionsoccurringis constantwith time. In a critical assembly, the raticlof the number

of neutronsproduced to the numberof neutronsdisappearingis commonlycontrolled

by the use of “poison”control rods (material that absorbsneutrons). Typically there

are two basic mannersin which neutronsmay vanish:

1. Absorptionduring a nuclear reaction

2. Leakage from the surface of the reactor

There are many methodsused to model the fissionprocess:

. diffusiontheory(Fick’slaw; differentialequations):a deterministicapproach

usingfinitedifferences

. MonteCarlo: a probabilisticapproachusing statistics

● transport theory (integralequations): a deterministicapproachusing discrete

ordinates

The simplest,most fundamentalapproachand the approachused early on in nuclear

system design is diffusiontheory.However, the MonteCarlo metho~ioffers improved

accuracyin modelingcomplexgeometriesand it has been the adapted method in the

current study.

1.1.3FissileMaterial

A materialis said to be fissile if it is capableof fissionat low energy levels (i.e.,

slow neutronswith low kineticenergy). 238U, which is abundanton the planet, is

used to “breed”fissileplutoniumby bombardingthe 238U with neutrons. Another

2

method used to create fissile material is the refinementprocess used to enrich the

percentageof235U innaturallyoccurringuranium.

1.1.4Prompt and Delayed Neutrons

More than 99 percentof the neutronsemitted in a fissioningsystem are emitted at

the instant fissionoccurs; these neutronsare called “prompt.”That fractionof a

percent of neutronsthat are emitted at a relativelylong time after the initial fission

event are called “delayed”neutrons.The averagenumber of prompt and delayed

neutronsreleasedper fissionevent is given the symbolV.

1.1.5 Cross Sections

A cross section is an experimentallydeterminedparameterwith units of cm2 which

indicatesthe probabilityof a certain event occurring.Differenttypes of cross section

data used in nuclearengineeringinclude scattercross sections,absorptioncross

sections,or fission cross sections.Cross sectionstake on the units of “barns”where

1barn = 1X10-24cm2. In essence, the nuclearcross section is the “effective”cross

section of the nucleus that a neutron sees when it is travelingnear the nucleus. The

total cross section is the combinationof the fission cross section, absorptioncross

section, scattercross section,etc., and is a measureof the probabilitythat any type of

interactionoccurs when a beam of neutrons impingeson a target composedof many

nuclei.

1.1.6Moderatorsand Poisons

A moderatoris a substancewhich tends to slow down (“thermalize”)neutrons.

TypicaJmoderatorsincludewater and polyethylene. A poison is a substancewhich

tends to absorb neutrons. Typical poisons includeboron and cadmium. Poisons may

be of the “burnable”type [14] which means their absorptioncross section decreasesas

time progresses(thus increasingthe reactivityof the system).

3

1.1.7 Over/Under Moderated Systems

A systemissaidtobe“overmoderated”if themultiplicationfactordecreases(i.e.,

criticalmass increases)with decreasingdensity (i.e., increasethe amount of

moderator).On the othel hand, if as the density is decreasedthe multiplicationfactor

increases(i.e., critical mass decreases),then the system is said to be

“undermoderated,”This informationis typicallyillustratedin a plot of muhiplication

factorvs. density (or equivalently,a plot of critical mass vs. hydrogento uranium

ratio).

1.1.8Promptand Delayed Criticality

Delayedcriticalityis used to describe the state of a fissilematerial ic which

the multiplicationfactor is unity from the contributionof both delayed and prompt

neutrons. Promptcriticality is a term used to describe the state of a fissile material in

which the multiplicationfactor is unity solely from the contributionof prompt

neutrons. Thus there is a “window”in betweendelayedcriticality (the steady-state

condition)and promptcriticality.’ This windowis given the symbol ~ and it follows

that the fractionof fission neutrons that are prompt is 1-$ This can be seen by

considering that a k of unity is due to both prompt and delayed neutrons; therefore,

+ ‘—)p<o (Do

k=l k = 1/(1-~)DelayedCritical PromptCriticalp=o P=P

Figure 1-1 : CrMcality Window

IIf notfor thjswindow,bombswouldberathereasytobuildwhile nuclearreactorswouldbemoredifficult; asit is, thereverseistrue.

4

to get rid of the delayed neutrons,we subtract the reactivityamount P. One may

question the validityof subtractingthese two values since at first sight they appear to

be different units; however,at closer inspectionit is apparentthat the units are dentical

since the reactivity~ is simplythe change in k whichhas been normalizedin ccordance

with value of unity at delayedcritical.Therefore,the multiplicationfactorconsidering

only prompt neutrons is ( l-~)k. When this value is unity, the system is said to be

prompt critical since a multiplicationfactorof unity is reachedwith only prompt

neutrons.

1.1.9Reactivity

Reactivityis definedas the percentagethe system is abovedelayedcritical:

k–1P~=

Thus, negativereactivityindicatesa systemthat is below delayedcritical while positive

reactivityindicatesa systemthat is abovedelayedcritical. Typically,the reactivityis

expressed in “dollars”(or fractionsof a dollar: “cents”)by using the conversionfactor:

~ reactivity= 1dollar. The value ~ is the differencein reactivitybetweendelayed

critil dity and prompt criticality. Thus, if a systemis promptcritical, then p=~

(remember,if the systemis delayedcritical, then the multiplicationfactor is one, and

the reactivity is zero).Typically,the texm“addingreactivity”is used when the system

is already at delayedcritical (i.e.,k=l, p=O).

1.1.10 Atomand NumberDensities

Typically,numberdensitiesare used for MonteCarlo input files to define the

materialcharacteristics. The numberand atomdensitiesare defined as follows:

5

N - ~NA= atom density = atoms I cm3M

atomsnumberdensity = (N )(1x10-24cm2/ barn)=

barn--cm

where:

NA = Avogadro’sNumber

M = molecularweight

1.1.11ScramSystem

A scram system refers to an electro-mechanicalsystem which produces a prompt

decreasein reactivitydue to physical movement. For example,a scram for the uranyl

nitrateexperimentwouldconsist of quickly moving the two fissileslab tanks apart

from one another to quicklydecrease the multiplicationfactor. TypicaI1yboth

automaticand manualscramsystems are designed into critic?l experimentapparatus

(the automaticmechanismsare coupled to particle detectors located around the

experiment). In addition, for the experimentproposed in this study, an additional

gravityassistedscram mechanismmay be incorporated. Althoughthis document

focusesonly on the primarymanualscrammechanism(a hydrauliccylinder),it should

be noted that two such redundantscram systems will also be incorporated:one

automatic,and one gravity assisted.

1.1.12HistoricalPerspective:LACEF

The urgency of World War 11that spurred the Manhattan Project also demanded

that a site be establishedat the Los Alamos National Laboratorywhich would serve as

an area for experimentalwork as well as isolate the populationfrom radiation in the

event of a criticalityaccident [12].The area chosen was in Los Alamos’Pajarito

Canyon and came to be known as “PajaritoSite.”Before 1947,critical experiments

were performedat the site by hand. This changed when, in 1946,Louis Slotin was

6

killed as a resultof a componentof an assemblyslipping into a more reactiveposition

producinga superprornpt-criticalpulseofradiation.As a result,thesiteestablished

much more exactingrules governingthe operationof criticalassemblies,one of which

was the policy of performingmost criticalexperimentsremotely.Suchexperimentsare

now performedin what are called “kiva..”:2buildingshousingcriticalexperimentsthat

are controlled from a remote location. The control systemoutlined in this document

will serve as the main control system for the original “kiva”which is now referred to as

KIVA I. Figure 1-2displaysa plan view of PajaritoSite. Today LACEF(Los Alamos

CriticalExperimentsFacility)housesthe mostsignificantcollectionof critical

assembliesin the westernhemisphem. The assembliesthat may be operatedat LACEF

can be divided into three categories:

. BenchmarkAssembliesare configurationscontainingpreciselyknown

componentsthat have interchangeableor adjustablefissilecores and reflectors.

. AssemblyMachinesare generalpurposeplatfoms into which fissile,

moderating,reflecting,and control componentsmay be loaded for short range

studiesof the neutronicpropertiesof the materials. The assemblymachine

describedin the followingsection falls into this category. IKis worth noting

that assembiymachinesdo not actuallycontain fissilematerial;they only

manipulateit.

● SolutionAssembliesallow criticaloperationswith fissilesolutions. The

experimentproposed in this study is a solutionexperimentmountedon an

assemblymachine.

2~c HoPi Indiannamefora roundceremonialchamber

7

1.2 Objectives

The main goal of this project is to create a numericaImodelof a fissioningsystem

(“criticalassembly”)using a well-establishedcomputercode and then bring togethera

systemfor controllingthe assemblybasedon the resultsof the numerical study.

Althoughthe numericaIresults will be specific to a certain criticalexperiment,the

control system will be inherentlygeneraland may readily be used to control other

experiments(specifically,an experimentinvolvinga steppermotorand hydraulic

system). In order to address the specificdetails that must be consideredwhen sizing

and selectingcontrolcomponents, a complete sizing analysis for the proposed system

is given in chapter seven. An introductionto the proposedexperiment follows.

T -“. ..’SJEbo..”’Kivo”i..

Bldg. PL-23 ● . ~ ‘ T

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.‘, -. ., RYjcxito, / ‘, ”., .,.:: - ,;. ,,.. .“ . .‘- . Rood. . , . . . .. . . . . . /!? ‘, ~,““ .: : - ,,.. ..- . . ●‘.Fuprito-n “. “. .

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. ......● .* -.. ,\~., “. . .,..’ . . .., . -.

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. ● ✎✎ ❞✎✎✛✌ ✞� ✌ ✎✌ ✌ ✚

8

Figure 1-2: Pajatio Site (TA-18)

1.2.1MechanicalSystem

‘I”hesystemchosen for study is a uranylnitratesolutionsystemin cylindrical

geometry. The experimentconsistsof two “slab”tanks filled with highlyenriched

uranyl nitrate,U02(N03)2, that must be pushed together remotely. The general

mechanicalsetup for achievingthis is shownbelow [11].Note that the detaileddesign

of mechanicalcomponents(e.g., supportbrackets or translationtables) has been

omitted in order to focus attentionon the two systems of primary interest from a

control system point of view: the stepper motorfleadscrew combinationand the

hydraulicsystem.PoisonMakrial (orGravityAssisted-

Movabkslabrank

sWr8mrorilrad~ oIlydradic cylidcr (Supplrrtfnma Orniaedfwchrily) (SupyrortfmrresomiucdfordAy)

,“” 3EE5L

SideView FrontView

Figure 1-3: Systems Overview

A hydrauliccylinder is used to push the movablecart toward the stationary tank.

Once the air gap betweenthe two tanks is decreased to a preset distance, the hydraulic

cylinder is shut down and the final approachto critical is made with a stepper motor

and lead screwthat drive a linear translationtable (upon which the moving tank sits).

The steppermotorlleadscrew combinationis used in favor of the hydraulic system for

finalclosure in order to increaseresolution(as will beeome evident in the following

chapters,such a systemis extremelysensitiveto small changes in the air gap). This

document focusesonly on the control of the stepper motorfleadscrew and hydraulic

systems. A completespecificationof all the syste~~ necessaryto perform the

experimentwould involvedesigning the frameworkfor the secondarygravity assisted

scram system (general concept illustratedin Figure 1-3)as well as all of the detail

design for componentssuch as mounting bracketsor mechanicalinterfaces(e.g., the

lead screwh.ranslationtable interface).

1.2.2HydraulicSystem

Figure 1-4below showsthe simplifiedhydraulicsystem circuit that is used to

control the hydrauliccylinderportion of the assembly [10]. Basically,the pressure

differentialm the cylinder is controlledby runningline pressurethrougha series of

three normallyopen or normallyclosed control valves.s

vI

No. ACC.

1

N.C.1

— IN

Figure 1-4: Hydraulic System

3Nom~]y open:whenpowerisofc,thewdveisopenNormatlyclosed:whenpowerisoff, thevalveisclosed

10

1.2.2.1Valve$

A total of three valves are used to regulate the pressure throughout the system.

When N.O. is open and N.C. 1and N.C. 2 are closed, the system is scrammed. When

N.O. is closed, either N.C. 1or N.C. 2 can be opened dependingon the speed desired

(speed is set by needle valves associatedwith N.C. 1and N.C. 2). When all of the

valves are off, the hydrauliccylinderis inactive.

1.2.2.2Accumulator

The accumulatorserves as a power source to the hydrauliccylinder in the case of

power loss. If power is lost, the normallyopen valve connectingthe accumulatorto

the scram line will open and N.C.1 and N.C.2will close,causingthe assemblyto

automaticallyscram.

1.2.2.3Pressure Switches

Two pressure switches, identifiedby PS1 and PS2, are used to check the

accumulatorpressure range and the scram line pressurerange. When a Iimit is

reached, the switch is activatedon.

1.2.2.4PumD

The pump provides the pressurenecessaryto move the hydrauliccylinder and

pressurize the accumulator. For the purposesof the control systemthat will be

discussed in the followingchapters, it is assumedthat controlof all hydraulicsystem

components requires 10-60volt DC power.Therefore,as will be made clear in the

followingchapters, the only type of control system output device needed is a DC

output “module”to send the appropriateDC voltage to the desired valve or pump.

11

1.3 scow of Study

This study completesthe preliminaryconceptualwork necessary for conductinga

criticalexperimentinvolvinguranylnitrate in cylindricalgeomet~ usinga horizontal

split table and, in essence,proves that such an experimentis feasibleby outliningthe

hardwareand softwarenecessaryfor conductingthe experiment.The scope of this

study includesthe conceptualdesignof the main mechanicalcomponentsas well as the

system needed to control these components. Detaileddesign of mechanical

components is outside the scope of this study and is taken as a “given.”

1.4 Report Outline

This report begins with a numericalstudy of the physical system to be controlled.

Next, the mechanicaldesign requirementsare outlinedand the conceptualmechanical

design that fulfills these requirementsis illustratedand brieflydiscussed. The

hardwareneeded to control this physical system is the next general topic addressed. In

these chapters ( chapters four, five, and six), the approach to control and the control

system componentsare discussed and introduced.In chapter seven, the results of the

numericalstudy are used to size hardwarecomponentsfor the experiment. In chapters

eight and nine, the softwareused in conjunctionwith the control hardware is

discussed. Finally, in chapter 10,a cost analysis for performingthe experiment is

presentedand discussed.

12

Chapter2.

THENUMERICALSTUDY

2.1 Introduction

Numericalstudies(as well as any availableexperimentalresults)will give an idea

of the characteristicsof the physicalsystembeingcontrolledand yield such design

informationas: how fast the systemcan be moved together, what kind of torque is

needed,and whatkind of control systemhardwarek needed to satisfy all of the

specifications. Used for this purpose,the Monte Carlo method (MCNP) is briefly

discussedhere and numericalresults for the experimentintroducedin chapter one are

generated.The data generatedhere is used to size a stepper motor and the peripheral

electrical&vices needed for the uranylnitrateexperiment. An admittedlysimple

modelof a uranylnitrate solutionsystemin cylindricalgeometryhas been created;

however,at this level of design, it is sufficientto corroborategeneral trends in data

froma previouslyconductedexperimentinvolvinguranylnitrateand similar

geometry.This numericalstudy is the fmt step in the followingprogressionof events:

● MCNP studies to determinevalues needed for the sizingof basic control

systemcomponents

● control system componentsizing: stepper motor, stepper motor drive

● componentinstallation

● programmingand debugging

2.2 The Monte Carlo Method

The methodof solving governingequationsby statisticalaccumulation(playinga

“game”)is used in many areasof scienceand engineeringincludingconductiveand

radiativeheat transfer, turbulence, and most pertinent to this paper, neutron physics.

The MonteCarlomethod involvesa physicalprocess that inherentlyexhibits some

form of randomness.The terms “randomwalk”or “Markovchain”often arise in the

discussionofsuchprocesses.Strictlydefined,a Markovchain is a seriesofsequential

events for which the probabilityof each succeedingevent is uninfluencedby prior

events [16].From this definitionarose the term “randomwalk”: an expression

describingthe randomnesswith which a dmnk man ambles down the street.This

random walk phenomenonis present nearlyeverywherein nature:

● the directiona bundle of photons is emitted during a radiativeheat transfer

process can be modeled as a random process

● the generationand death of vortices in turbulent fluid flow can be seen as a

random process

. the life and death of a neutron during the fissionprocess can be modeledas a

random process

Thus, any seeminglyrandomprocesscan be modeledas long as one critical piece of

experimentaldata is available: the frequencydistributionof the event or events. For

example, in a game of darts, the frequencyof a dart hitting at some radial positionon

the dart board may be graphicallydisplayedby plottingfrequency(i.e., numberof

times the dart hits) vs. radial position on the dart board.

14

Figure 2-1: A Dart Game Witha HypotheticalFrequency Distribution

Typically,thefrequencydistributionismathematicallymanipulatedintermsofmore

convenientfunctionssuch as the “probabilitydensity function”or the “cumulative

distributionfunction.”For instance,if the frequencydistributionis denoted by f(~)

then the probabilitydensity functionis foundby normalizingthe frequencydistribution

(i.e., dividingby the area under the j(<) curve):

p(g)= , f(~)Jf(E)4u

So if random numbersare chosen for& the resultingdistributionmust resemble that

defined by the equationshown above. In other words, we may create a probabilistic

model that repeatedlyplays the same “game”utilizingrandomnumbersand physics.

However,those random numbs must agree with the probabilitydensity function that

is observedin physicalrealityand definedby the generalequation shown.

2.3 Las Alamos National Laboratoryand Monte Carlo

The Monte Carlo methodemerged from work done at Los AlamosNational

Laboratoryduring World War II and the inventionof the method in general is

attributedto Fermi, Von Neumann,and Uhun. This initial work on the Monte Carlo

methodeventually led to what is now known as MCNP: the Monte Carlo Neutron

Photon computer code [6]. MCNP is a general purpose Monte Carlo code that can be

used for neutron,photon, or coupled neutron/photontransport and is generally

recognizedas one of the best codes in its class since it incorporatesstate-of-the-art

physics,data, and mathematicalmethods.

MCNP followsthe entire life of manyparticles from life to death; the “game”

15

(fissionprocess) is startedby a sourceof freedstrength specifiedby the user. When

run in neutron transportonly mode, there are four possibleevents a neutron can see

duringitslifetime:

1.Neutron scatter

2. Fission

3. Neutron capture

4. Neutron leakage

MCNP simply followsthe entire life of each particleby randomlyselectingone of the

possibleevents (and, if scatter is selected, a rdndomdirection)based on a set of rules

(physics)and probabilities(transportdata) governingthe processesand materials

involved.As the lifetimehistory of more and more neutronsis followed,the

distributionof neutrons is better known. Typical fission cross sectiondata for 235U

and other fissile materialsis shownon the followingpage [15]. In addition to fission

cross sections,other cross section data is used by MCNP includingscatter, absorption,

and capture data. As seen on the plot, 235U has a much higher probabilityof fission

occurring when the neutronsare in the “thermal”(i.e., ambient temperature)region

rather than the “fast”(i.e., greater than ambient temperature)region. In between the

thermal and fast regions, the probabilityfor fissionfluctuatesgreatly; becauseof this,

nuclear systemsare commonlyreferred to as being in one of two distinct states: “fast”

or “thermal”(the system is forced to be thermal or fast by design).

2.4 Input File Overview

A typical MCNP input file is composedof four major sections;each section being

composed of a number of input “cards”(horizontalrows of data). The four major

sections are:

. Geometryspecificationcards

. Surfacespecificationcards

‘F----”:”’

//.’

.’

17

● Importancecards

● Materialspecificationcards

● h4CNP“mode”cards

● Tally cards

Each of these sections is discussedin moredetail in Appendix A.

2.5 Uranyl Nitrate Solution System

A simple modelof a uranyl IIitratesolutionsystemin cylindricalgeometryhas been

created. The geometryused in the study is shown in Figure 2-3 and the [naterialsused

in the model are defined in Table 2-2. This geometrywas created by defining a total

of 13surfaces,nine of which were planes normal to the Y axis; three were cylinders

centered on the Y axis, and two were spheres centered about the origin. The cells

were created by defining the appropriateintersectionand union of surface senses as

explained in AppendixA. The two cylindricalslab tanks were sumoundeciby a

sphericalshell of six inch concrete;air was placed inside this sphere and around the

tanks. The importanceof the sphericalregion of interestwas assigneda value of one

v$ile everythingoutside that region was assignedan importanceof zero. The numtxr

densitiesused for the uranyl nitrate solution were calculated assumingthe data shown

in Table 2-1 (see AppendixB for the calculations)[4] while the numberdensities for

the remainingmaterialswere taken from publishedliterature [17] (in reality, atom

fractionswere entered; but as explainedin AppendixA, this is equivalentto number

densities). While not to be used in practice, the concrete shell was used in order to

crudely model any reflectioneffects from surroundingwalls.

18

28.5”DIA. I

27.ti”DIA.

Spherical shell made from two spheres

H w+4.48”Lh’i@ Nitmc .487”30%Bond Po]y

H

Figure 2-3: Slab Geometry

Table2-1 : Assumed Valizesfor Number Density Calcukztions?-

SolutionConcentration:405.2 gll

NominalOveidl Densityof UranylNitrate: 1.558g/cc

Solution Acid Content: .32 Molar (HNO~)

Enrichment:93.1 % 235U

5.9% 23%

1% 23%

8 for 2%J = .M7

2(I

Fission products such as 236U were not included in the model since the affect on

the fissionprocess has beenassumed negligible. In addition,other extraneous

elements that might be present in solution such as Fe, Na, or Al were not modeled.

The generalgoal of this study was to determinethe system sensitivityby varying the

air gap betweenthe two tanks, thereby revealing limitationsand characteristicsthat

must be consideredwhen assemblingthe control system.

Table2-2 : Model IUatcwiaic- —-.. - - . ------- ... . . . . —-

Material Composition NumberDensity(atoms/barn-cm)

UranylNitrate Solution 234 1.W33X1O-5 —235; 9.67I9x1O-4238u 6.0521X10-5

H .0544393850 .03600846N .00226872

StainlessSteel c .000317Cr .016471Mn .001732Fe .06036Ni .006483Si .001694

Concrete H 1.4868x10-2c 3.814x10-3o 4.15I9X1O-2Ca 1.1588x10-2Si 6.037x10-3

Mg 5.87x10-4Fe 1.968x10-4Al 7.35X1O-4Na 3.O4X1O-4

(table continues)

Air Ni .7840 .211Ar .005

30 wt% Berated Poly H 5.19X10-2c 2.O6X1O-2B 3.54x1O-2

2.6 Results

Figures 2-4 and 2-5 show the results of the air gap study. All values of I+ff shown

are at the 68% confidence level.The ~ff valuesshownhave been calculatedby

combiningthree separateestimationtechniquesthat MCNPemploys (collision,

absorption,and track lengthestimates).The followinggenera!characteristicsof the

model are noteworthywhen a comparisonwith experimentaldata is made:

● model does not include fissionproductsor other elements such as iron,

aluminuin,or sodium that could be present in solution

● modelgeometrymay differ slightlydue ambiguitiesin someexperimental

dimensions

Keff Vs. Alr Gap99

‘-0’0~MONPRooulm

flmsnt Rooults

0.0s0}’r

~9

-:----

7’-----.+...0.980

1.--%:+..-““l‘....>.>=

0.070

0900 L-m-T&A0.ss o.4a 0.6s o.ea o.7a o.8a o.sa t.oa I.w

AIR OAP (Inohoo)

Figure 2-4: Keg VS.Air Gap

21

I?eactlvlty Vs. Alr C3ap

0 MONP ROSU180- •lmll~f espcrtmon8 nDowlts

4.QOOO--—-—–——-—— ,4● % - 1.a4a - 2 /808 r-2 - 0 000

0.0000 - -.i -=-...,, .=

-1.0000

}

.. ,

““”-\-.,

f-2.0000 ‘=...---:--..>..

=E-

, L------ ‘--s.0000 -d I‘\ ““-..........

4

/?,‘\\ :;K-.

-4.0000 -= b’ ‘-”- ‘1-i y - -o. B2e - 2.890X r-2 - 0.6s4

-6.0000 ! II 1 I I , 1 r I 1

0.s3 0.43 0.63 0.03 0.7s O.ea 0.0s 1.0s 1.13AIR ~AP (Inuhoo)

Figure 2-5: Reactivity vs.Air Gap

The results shown are within two percentof similarexperimentalresults for uranyl

nitrate in slab geometry. Althoughthis error might ii~kkdly appear small, it is

enormous in terms of criticality. For example, a 1.426percentemor in ~ff translates

into approximatelytwo dollarsdifferencein re~ctivity:a differencebetweenthe system

being well subcriticalVS,the systcm beingdelayedcritical; refer to air gap= .45”on

Figures 24 and 2-5. While the experimentalreactivityat this separationdistance is

ze]’o,the reactivity from the MCNP study is calculatedas:

= -2.07 dollars

TJ

Duetotheextremeeffectsofsmallchangesin!+~,anymodelthatwillbeusedto

predict criticalitymust preciselyaccount for the effect of each material in the general

vicinityof the fissioningsystem. This was not the case for the exjxximentaldata

referencedhere; the model does not preciselyaccount for all materialspresent in the

actual experiment. So why model the system in the first place? Althoughthe

informationshown in the two figurescannot (and absolutelyshould not) be used for

criticalityprediction,it can be used for sizing the control system. This is because,

:d[hw]~k the MCNP resultr arc offset h:-I !heexperimentalresults. the slope oi the

MCNPdata is in approximateagreementwith the experll.i~,. . ..!ts.In fact, the

Monte Carlo results yield a 4.5 % conservativeestimate for the slope of the plot. This

means that the maximumrate at which the assemblywill be allowedto move (as

definedby the conservativeestimate)will be slowerthan the actual maximumspeed

allowable(as definedby the experimentalresults).In this case, we were lucky since

there were experimentalresults with which to compare the numericalresults. If an

experimentwere to be performedwithout such a luxury, we would need to

painstakinglyensure that the model resembledthe physicalsystem as accuratelyas

possibleby modelingeach materialpresent in the experimentexactly (e.g.:exact

dimensions,exact solutioncomposition).

Nominallyfour to five millioncollisionswembankedwith approximately 140,000

neut.mnsgeneratedper run. In assessingthe results of these Monte Carlo calculations,

a distinctionis made betweenprecisionand accuracy. Precisionis the uncertaintyin

the average valuecalculatedby the program itself. Accuracy,on theother hand, is a

measure of how close the calculated result is to truth. Jr other WO’-k, results may be

precise and not veg accltr: ‘f r .’onv .~!’iymi,- be:’ ‘( TaItZ’and ‘0[ very prcCi~. In

Ilnc]udingthe~ssiblc presenceof unventedradiolyticgws

-)3

thiscase,sinceweknowthatthetruthfulvalueisapproximately10.89centshm based

on previousexperimentswith the uranyl nitrate packages,we may conclude that the

model predictionof 11.38centshmn is very accurate(.49 cents/mmconservative)

despite the lack of highly detailed modeling. The precisionof the data shown is at the

68% confidence level; in other words, if 100runs are performed,then 68 of the values

(one standarddeviation)will fall within the precisionbars shown on the plot. While

the data shown is not extremelyprecise, the numberof cycles performed(50 cycles

with a nominal 3000 neutronsgeneratedper cycle) is considered large enough to result

in adequate accuracy. Therefore, the numerical results shown here corroborate the

slope measuredfrom experimentand suggest a moreconservativeestimate for sizing

the control components. This is the estimate that will be used in chapter eight.

2.7 Summary

The Monte Carlo studies performedindicate that approximately 11.38cents of

reactivityare added for each millimeterof closure betweenthe tanks.This value

conservativelycorroboratesthe experimentallymeasuredvalue of 10.89cents per

millimeterand, in general,providesan estimate for how muchexcess reactivityis

present in the system (i.e.,how sensitivethe system is to smaJldisplacements). As will

be shown in chapterseven, these valuesset the maximumallowablevelocity,the

stepper motor and drive type, the lead screw pitch, and the gear reduction ratio.

24

r

Chapter3.

COWEP’I’UALMECHANICAL DESIGN

3.1 Basic MechanicalRequirements

While it is not the goal of this study to provide the detailed drawings for

manufacturingexperimentalapparatus.the mechanicaldesign aspect of the project

must neverthelessbe addressedon a conceptuallevel. The fundamentalmechanical

requirementsfor the experimentincludethe following:

. Two frames must be de~ignedthat will hold eaeh of the two cylindrical tanks.

Reflectionfromthese framesmust be held to a minimum;therefore,a minimum

amountof materialtiwts!illprovidesthe greateststabilityand reliabilitymust

be used. Since the mean free path of aluminumis relativelylarge, this material

is somewhattransparentto neutrons and would serve well for the application.

. A translationdevice must be designedor purchasedthat will be driven by a

stepper motor upon which the movingslab tank will rest.

. Adjustmentdevices must be designedor purchased in order to adjust the

relativeslab tank positions.

The main requirementscan be summarizedby the need to secureboth slab tanks on

each cart with the maximumadjustmentcapability(positionalfine tuning) and the

minimumneutronreflection. Since these goals are contradictoryin nature, a number

of design iterationswill be necessary;a conceptualdesign to begin the process is

offered in this chapter.

As seen in Figure 3-1 on the followingpage, the “honeycomb”structure is a lattice

of extruded aluminumtubes that were placed together for a previousexperimenton

the horizontalsplit table referred to as “Honeycomb.”

25

26x 243.in. quxm Al Idah

Figure 3-I : Current Expen”mentalConfiguration(“Honeycomb”)

This is the cumentconfigurationof the experimentalassembly;as shown,the extruded

aluminum tubes are held in place by four clamp %x. The next section discusses the

options availablein fit~.ingthis split table for the slab tanksexperiment.

3.2 Options for Performing the Slab Tanks Experiment on Honeycomb

There are two options that may be considered when approachingthe conceptual

mechanicaldesign. The first is to mount the tankson the existing split table with the

honeycombstructures in place. The second option (Figure 1-3)is to take the

honeycombstructureoff of both tables and design space frames for each tank from

scratch (as opposed to retro-fittinga design to the existing honeycombstructure). The

latter of these two options is preferablesince positioningof the slab tanks maybe

accomplishedin a much more precisemanner using this approach. As the numerical

studyclearly indicated,the system is exfremelysensitiveto small changes in tank

position; therefore,relativelysmall toleranceson the order of .001 inch must be

imposedon the mechanicaldesign. Ahhough this avenue is more costly, it provides

for greater experimentalaccuracysince positionaladjustmentsmay readily be designed

into the structure from the outset. The advantageof removing the Honeycomb

material is particularlyevidentwhenconsideringthat locatingany singlepoint within

the lattice is achieved at best with large uncertaintiesdue to the structure’s

26

constructionand the originalexperimentalintent: to mockuprelativelylargecritical

systemswith inherentlyloose tolerances. As seen in Figure 3-2 below, the tank would

ideallyhaveadjustmentcapabilitiesintheX,Y,Z,THETAX,and THETAZ

directions in order to ensure proper tank alignmentand increaseexperimental

flexibility.Whilethis goal is ideal,cost and fabricationconstraintspracticallylimit the

adjustmentfeatunx to a minimum:the X and Y directions.z

THETA Z

-x-x

t

z

I

Figure 3-2: Adjustments Ideally Avaikble for Sikb TankAlignment (Sikb Tank onMovable Cart)

Adjustmentin the Y directionallows for final closure via a steppermotorfleadscrew

attachedto a translationtable while adjustmentin the X directionoffers fine

adjustmentto ensure the tanks are not offset with one another. The remaining

adjustmentaxes shown must be fixed accuratelyby the mechanicaldesign itselfor

adjustedwith shims.

27

3.3“MechanicalDesign Concepts

Table 3-1 displays the generaldesign philosophyfrom the mostessential,basic

functionsat the top, down to the less essential but no less desirabledetailed functions

at the bottom. Included in this table are likely hardware solutionsto the desired

functions.

Table3-I: Mechanical Function an

FUNCTION

Tank securityand stability

Roughtank movementover a relatively

Ionz distance

Fine tank movementover a relatively

short distance

Tank alignmentadjustmentin the X

direction

Tank alignmentadjustmentin the Z

direction

Rotationaladjustments

Solution From Most to Least Essential

SOLUTION

Rigidaluminumspace frame

Hydrauliccylinder

Stepper motor/lead screw

Micrometerhead/leadscrew device

(figure 3-3)

Micrometerhead/Ieadscrew device

(figure 3-3)

Rotationaltable/micrometerhead device

Micrometer x

Figure 3-3: MicrometerA~”ustmentwith a Lead Screw Concept

28

Figure3-4 belowillustratesone possibIemechanicalconfigurationfor achievingthe

minimumrequirements. In this option, two translationtablesare essentiallystackedon

top of one another in order to provide for the X and Y translation. A micrometerhead

is used as the means for adjustmentin the X directionwhile a stepper motor is used to

achievefinal closure intheYdirection.Figure3-4 presentsone feasibleoption for the

mechanicalhardwareconfigurationand is not intendedto be exclusiveof other

configurationsthat may be equally viablesuch as differentspaceframedesignsor slab

mountingmethods. The followingchaptersdiscusshow such a system will be

controlledremotelyand assumea given mechanicalconfiguration.

XTr+ioII Table

),

, I( I

Imuknl r@bMAd.saEw

\

r 7 ———

lid

pJ I 0 1[ MOVABLE CART 1 I~... 1

FrontView SideView

Figure 3-4: An @ion for the Mechanical Con#igumtion

29

Chapter4.

APPROACHES TO EXPERIMENT CONTROL

4.1 General Mode of Operation

After determiningthe basic systemparameters(namely,the system’smechanical

design and change in reactivitywith linearposition),we are in a positionto consider

the control system. Typically, the control system used for critical experimentswill not

operate using PID type automaticcontrol and will not require the extremely fast

response found inhighperformanceservo-typecontrol systems [8,19].Instead, the

system will incorporatesimple feedback to verify the state and positionof output

devices;this is the simplestsystemthat achievesconsistentand reliablemechanical

control. Although feedbackis present in such systems (opticalencoder,

thermocouples,etc.), it will generally not be used for proportional type control of an

experiment(as indicatedby the dashed line in Figure 4-1 below).This restriction is

dictatedby current DOE enforced technicalspecifications.

t I

I I I

I

!L — ——— —— ——.--Eiizl-----

————IIIII

I————

Figure 4-1: Blbck Diagram of the General Control System

30

4.2Digital Vs. Analog

In the past, control of criticalexperimentremoteassemblymachineshasbeen

achievedthroughthe use of hard wired control systems.Althoughsuch systems have

proven reliable, the advent of the powerful,dependable,low cost, microprocessorhas

madedigital systemsa very lucrativeoption. Uniikehardwiredsystems,a digital

control systemoffers the flexibilityof quicklyand easilychangingthe controller

characteristicsby simply re-writingthe control program.For example, if the estimate

for the slope calculated in the previous chapter is later found to be too conservative,

the closurevelocitymay be easily changedsimplyby re-writinga few linesof code.

This flexibility,combinedwith increasedpowerand reliability,has propelledthe digital

control system past its hardwiredcounterpartfor critical experimentcontrol

applications.There are two avenues that might be pursued when controllinga system

digitally:a custom designedsystem,or an off-the shelf purchasedsystem.

4.3 Custom Digital Systems

The first option involvesdesigning the entire control systemaround a single

microcontrollerchip. Typically,such chips contain on-boardmemo~, timers,ports,

and other support functions that would normally require separate IC chips.

Customizedmicrocontroller-basedsystemsoffer the followingadvantagesto the

potential user:

. control of the system and softwareat the machine languagelevel

. increasedflexibilityto meet exoticdemands

On the other hand,customizedsystems involvethe followingdrawbacks:

. the system is harder to maintaindue to its increasedcomplexity

● to construct such a system requires a PROM burner and other additional

peripheralhardwareinvestments

31

● debugging,maintenanceand constructionrequiresspecializedknowledgeand

experience

Thus, for specializedapplicationsdemandinga largedegree of flexibilityin control, a

customizedsystem may be appropriate.

4.4 PurchasedSystems

The other alternativeis to purchase a pre-manufacturedmicroprocessorbased

system, typically referred to as a ProgrammableLogic Controller (PLC) [13], from a

vendor. This alternativeis preferredin the nuclearcriticalityarena because in-depth

documentationand verificationof control systemreliabilityis greatlysimplified.

Unlikemost customizedsystems,pre-purchaseddigital systemsoffer relativelysimple

programmingsoftwareand allow for more efficient andthorough maintenance.For

these reasons, it was decided to purchasea PLC system from the Allen-Bradley

corporationrather th creating a customizedcontrol system. This control system is

introducedin the followingchapter.

32

ChapterS.

CURRENTCONTROLSYSTEMHARDWARE

5.1 Introduction

Currently,Control Room One at LACEF is fittedwith a digital control system

that was originally installedto control the SHEBA(SolutionHigh Energy Burst

Assembly)experiment(see Figure 1-2). Specifically,the systemis manufacturedby

the Allen-Bradleycorpmtion and incorporatesconvenientsystem modularitywith a

simplegraphicalprogramnu“nglanguage. An overviewof the typicalphysicalsystem

to be controlled is seen below in Figure 5-1.

MICROPROCESSORCONTROLPROGRAM

HYDRAULICSYSTEMS SCRAMSYSTEMS MECHANICALSYSTEMSValvesMotorLimit switchesPressureswitchesControl switches

PneumaticcylindersValves

Stepper motorEncoder/ResolverTableMountingbrackets

Figure 5-1: T~ical Cri&al Assembly ControlDevice Requirements

The main goal of this sectionof the study is to assemblea functionalcontrol systemon

a test bench that will allow for programdevelopmentand hardwaretesting without

intrusionon the current system in Control Room One at LACEF.With such a system,

the followingtypes of devices maybe tested:

. DC stepper motors (with two different approachesto their control as discussed

later)

. digitallycontrolledday contactdevices

. AC synchronousccnstant speed motors

The devices shown in Figure 5-1 are basic to controllingmany types of critical

assemblies.An assemblythatrequiresrotationalortranslationalmotionwillemploy

one or all of these devices in addition to the peripheralcomponentsthat form the

backboneof the control system; these peripheralcomponents makeup the test bench

control system that is described in the followingpages. In chapter seven,expansionof

law controlPlonselectcx Module rack

/

CloseddrcuitTV and inct&tmGghts Additic)nd1 . Ma (X@smOn

34

I-4 I I ! t ! I/ I I

I

v L I I RAPunit-1 JoysWk \ \Con?ldlel

v.-

I Nw

Ci%%2.s‘am \Cmlputergenefoted

stat-up controlcS@oy

pink%

L

\

Figure 5-2: Current Control Room One Configuration

the control system thatisalreadyin use in Control Room One to includeexperiments

in IUVA I is discussed.This chapter, as well as the next, form the groundworkfor the

eventualexpansion into KIVA I (note in Figure 1-2that the SHEBA building is

separatefrom IUVA I; the SHEBAbuildingcurrentlyemploysan Allen-Bradley

systemwhileKIVA1doesnot).Figure 5-2 onthepreviouspageshowsthecurrent

configurationof Control Room One.

5.2Test Bench ControlSystem

Shown in Figure 5-3 is a schematicof the control system test station that has been

setup at Pajaritosite. This system has been created from spare parts available from the

SHEBA system; when it is required to expand the current Control Room One system,

parts from this system may be used.The pwpose of the setup that currentlyexists is to

provide a platform for on-line programrningand testing that can be used to write and

debug “ladderlogic”programswhich will eventuallybe uploadedto the processor

UJCALW3CNA!LW 8 SUJTS.4GROWS(1~1.A2B) REMOTE W2CNASW% 12SWTS.4GROUPS(IT31-A3BIA)

o 1 2 3 4 5 6 7 8 9 10 I J2

O- 1771ASBREMOTElK3ADAPTER!-l ! =>WY IKJMODULESWTSJ2->120VACKJWERSUPPLY

0-178I=> 177LJBDIX JNPUlMODULE(I030V)2* 1771OBDm~~ MODULE(I06W)

o6!&swmsmFMm0R

3-> t731-lFEAANALIXJ JNPUTMODULE

46=> EMPTY 10MmuLEsm7* 120VACRXVSRSUPPLY

=“ REMOTEmCHAssJsJSNOTwlREDTOLKALCNASSISSINCE NOLX OU13Wl MODULES ARECURRWLY AVAILABLE FORTNLSPURPOSE

Figure 5-3: Program and Hardware Test Station

currently used in Control Room One. In addition, such a test platform serves asa

center for the test and evaluationof hardwarethat might eventuallybe used for the

KIVA I system.This separatesystem allows for on-line programmingand hardware

.,!,

familiarizationwithoutintrudkgon thesystemcurrmtlyinoperationinControlRoom

One.AsseeninFigure5-3,theassemblyusesadriverwhichcontrolsa steppermotor

attachedto a turntable;thisisoneof twooptionsfordrivinga steppermotor.

5.3ConfiguringtheSystem

Systemconfigurationinvolvedsettingdipswitchesonthetopandbottomofthe

PLC-5/15processormoduleand theI/Ochassisbackplane[1.2,3].Theseswitch

settingsdeftnedparameterslike:Aeracknumber,theI/Ogroup(usedwhen

programmingthePLCsystem),thetransmissionrate,andthepowersuppliespresent.

TheCompumotorAXdrivewasconfiguredby settinga singledipswitchassembly

nearthebottomof thecase[7]. Thisswitchassemblydefinedwhatkindof motor

(i.e.,currentrequirement)wasto bedrivenandtheaddressof theAXdrive(tobe

usedwhenwritinga programtobe storedin thedrive).

5.4 ComponentSumrn8ry

5.4.11785PLC-5/15Processor

Thisis theheartof thecontrolsystem.Thecontrolprogram(writtenin “ladder

logic”usingthe PLCsoftware)is uploadedto thePLC-5PROMfromthepersonal

computervia the 1784Kl”/Bcommunicationboard.A shorttestprogramutilizingtwo

switchesandLEDindicatorsavailableon theDCoutputmodulewaswrittento

validatethateachcomponentseeninFigure5-3isoperable[1].ThePLC-5module

seinesas themaincontrolmodule;thesolepurpw a; thePCis as a programming

terminalanddatamonitorstation(usingControlViewsoftware).ThePCdoesnot

directlycontrolanything.

37

38

h

5.4.21771 IBDDC InputModule

TheDCinputmoduleacceptsinputfromcommonDCdevicessuchasswitchesor

pushbuttonsandcommunicateswiththeprocessorvia the“backplane”(printedcircuit

board)locatedonreartheI/Ochassis.DCinputandoutputmodulesrequirea

separateDCpowersourceas seeninFigures5-3and5-4.Forthe KIVAI expansion

discussedinchzptersix,a DCinputmodulehasbeenplacedin the remoteI/Orackin

orderto providefor theoptionof a scrammechanismlocatedinsidetheKIVAitself.

5.4.3177] OBDDC OutputModule

The DCoutputmoduleis the logicalcounterpartto theDCinputmoduleand,like

allothermodulesin thechassis,communicateswiththeprocessorviathebticlcplane.

Theoutputmoduleis wiredto devicesrequiring10-60VDCpowersuchas lights,

seven-segmentdisplays,horns,or valves.

5.4.41771IFEA AnalogInputModule

As itsnameimplies,theanalogmoduleacceptsanalogsignalsfromrealworld

devices.Forcontrolof a criticaiassembly,thismodulewillacceptanalogsignak from

thepotentiometersthatmakeupthejoystickcontroldevice(a typicaljoystickis made

usingoneor morepotentiometers).Theladderlogicprogramwilldictatethedetails

of the interfacebetweenthejoystickandtheoutputdevice.Thismoduleis simplyan

analogto digitalconverter.

5.4.5120 VACPower Supply

Thisprovidespower(convertingvoltagefromACto DC)via thebackplaneto the

moduleslocatedin therack.A powersupplyof this typeis requiredforeachJ/O

chassis.

5.4.6 CompumotorAXLDrive

ThecompumotorAXLdrivecombinestwofunctionsinonepackage.First,it acts

asa pulsesource. Thisisbasicallya sourceof squarepulsewavesthatis usedto tell

thesteppermotorhowfarandfastit shouldrotate. Thesecondfunc!ionof the

Compumotorpackageis asa driveor “translator.”A translatortakesthepulsetrain

generatedbytheprogrammingcommandsandtranslatesi: intothevoltagenecessq

forenergizingthemotorwindings.Themotordrivemaybeprogramn,sdviaan RS-

232 port froma regularPC. Theprogramiswrittenina simplelanguagedeveloped

ky compumotorand is stored in the AXL’Sresident PROM (up to seven such

programs may be stored). A storedprogrammaybeexecutedviatheRS-232

connection,or, it maybeexecutedvia thePLCcontrolsystem.To runtheprogram

viathePLCsystem,onesendsa pseudoBCDnumber(3 bitsinsteadof four)to the

SEQI, SEQ2,andSEQ3linesof theAXLdrive. Dependingon thecombinationof

thethreesequences,oneof thesevenprogramswillbe run. Althcughthismethodof

steppermotorcontroloffersa greatdealofpowerandflexibility,thereis another

optionto steppercontrolthat ispreferred.Thisoption(a separatepulsesource)is

di.scusscdinthe nextsection.Theprogrammingthataccompaniestheintegrateddrive

isdiscussedinchaptereightas well. In thefuture,detaileddevelopmentsinclude

addingfollowingcomponentsto thesystem:

. encoderfeedbackmodule

. powercontactrelaymodule

● stepperpositioningmodules,translator,andnewsteppermotor

5.5Controlof DCStepperMotors

Often,anexperimentalapplicationrequiressmall,precisechangesin motion;thisis

typicallyachievedwitha DCsteppingmotor.A DCmotorusesdirectcurrentpower

‘#

inorderto inducea currentontherotorof themotorthatcausestheoutputshaftto

rotate [5]. This is accomplishedby theuseof a commutatorandbrush. The

:ommutatorisacylindricalobjectuponwhichthebrushesridetochangethedirection

of current in thewindingsin orderto keepthe rotorrotating.A “brush”is a pieceof

conductivematerialridingonthecommutatorwhichconductscurrentfromthepower

supplyto therotorwindings(stator). A “permanentmagnet”DCmotorusesa

permanentmagnetas thestatorinsteadof windings;windingsareusedforthe rotor.

Therearetwomainoptionsavailablefor thecontrolof a standardpermanent

magnethybridsteppermotor.The firstoptioninvolvespurchasingan integratedunit

froma manufacturer(liketheCompumotorAXLdrivediscussedin theprevious

chapter).Thesecondoptioninvolvespurchasinga standalonepulsesourcefromthe

ElPLCChassis

LPulse/kmslator StepperMotorsource

OptionI: CombinedPulseSource/I’ranslatofProgrammingLoadSplitBetweenthePLCandPulse/hanslator

PukeSource TranslatorStepperMotorPLC

Chassis

Option2:SeperatePulseSource,TranslatorProgrammingLoadConsolidatedtothePLC

Figure5-5: DCSte~er ControlOptions

40

PLCvendorandsendingthatpulsetrainthroughaseparatetranslator(i.e.,splitup

thetranslationandpulsegenerationfunctions).DCsteppermotorsarecontrolledby

varyingthepulseratesentto themotortranslator(or“drive”).Thetranslatorand

motoraresizedaccordingto thespecifictaskandthepulserateis controlledthrough

software.Asdescribedbefore, a translatorbasicailytakesthepulserate(generated

extemailythistime)and“translates”thepulserateintotheappropriatevoltage

necessaryto movethemotor.Thefirstof thesetwooptionswasrealizedon thetest

bench;however,it is preferableto consolidateallof theprogrammingandcontrolto

onlytheremotePLCchassis(insteadof programrningbothan integrateddriveandthe

PLCsystem).Forthisreason,a stepperpositioningassemblythatsplitstranslationand

pulsegenerationfunctionshasbeenusedin theControlRoomOneexpansionlayout

discussedinchaptersix.

5.6The StepperMotorDrive:Characteristicsandselection

Thesteppermotortranslatorcontainsthe logicnecessaryto “translate”thepulses

generatedby steppermotorcontrolassembly(indexer)intothecorrectvoltageneeded

by the steppermotorforshaftrotation.Thesteppermotorwillrotateonestepfor

eachpulsereceivedfromthecontrolleranditsperformance isve~ closelycoupledto

thetranslatorsperformance.If a lowperformancetranslatoris usedin conjunction

witha highperformancesteppermotor,theoverallperformanceisdefinedby the

lowestperformingdeviceanda costlymismatchexists. Translatorsmaybe purchased

tooperatein a numberof “ferentmodes;typically,full, half,or micro-stepping

mode. In thefullstepmode,the translatorwillstepthemotoronefullstepforeach

pulsereceivedwhileinthehaifstepmodethemotorwillbesteppedone-halfofitsfull

step(0.9degreesif themotorusedhas1.8degredstep). Microsteppingreferstoa

featurtfoundonmoreexpensivetranslatordeviceswhicharecapableofsteppingthe

motorby as littleas 1/125of thefullstepperpulsereceived.Thetranslatoralso

containstheciruitrynecessarytoopticallyisolatethehighervoltageareafromthe

controlsystem.

42

Chapter6,

CONTROL SYSTEM EXPANSION

6.1PLCSystemExpansionIntoKIVAI

Figure6-1showsa controlsystemdesignthatmaybe usedfor thecurrentPLC

controlsystemexpansionintoKIVA1.In particular,theconfigurationshownmaybe

usedto controlup to threesteppermotorsandwouldbe idealfora varietyof

experimentalsetupsincludingtheuranylnitrateexperimenton thehorizontalsplittable

“honeycomb.”

LOCAL

REMOTE\

\REMOTEIK3CHASSIS:12SKY2S.6GROUPS(1771.A3BI)

kpm’‘qf’’’-”’k” ACPowerin

Iwiw&1‘k!? \\

LOCALUOCNA.SSIS:6 SLOTS,4GROUPS(1771-A2B~o I 2 3 4 5 6 ‘7 8 9 10 1} )2

b 4

‘tI,

ACPawt

o=> 1771-ASBREM(YI’ELIOADAPTER

AL.

G!!9

I => 1771-IBDDC INPUT MODULE (IW30V)

2=> 1771-0BDCCOLIlT~MODU3X (10.6OV)

3=> 1771-MISTEPPERCONTROLLERMODULE4 -6=> 1771-OJPULSEOU1’PLtrEXPANDER

7-II m EM37Y LfOMODULESIXJIS12=> 120VACPOWER SUPPLY

C!i!!9I

ih’a!!\

\

\

I \>‘lo SsEm BUILDINGREMOIERACKS

0=> 1785flc-~is PROCFAW’OR \

1e IT?l-IBD DC INP~MODULE(10.30V)\

2=> 1771OBDDCOWPW MODULE IKMOV)3 = > 1711-lFEA ANALOGINPUl MODULE \

4.60 EMPTY UOM.C;JULESLOTS

7=> 120VAC POWERSUPPLY\

Figure6-1: AnticipatedKWA I ControlSystem

This layoutcontainsthe followingadditionalmodulesthat havenot beenused in the

43

testbenchsetupshowninchapterfive.

6.1.1 1771-ASBRemoteI/OAdapter

The remoteI/O adapterservesas a communicationlinkwith the localPLC-5

processor and communicateswith all of the other modules in its rack via the

backplane.

6.i.2 1771-A41Stepper ControlModule

Thismodulecontrolsthe pulseoutputthat is sentout to thesteppermotor.

6,1.31771-OJPulseOutputExpander

Onepulseoutputexpanderis requiredforeachsteppermotorto becontrolled.One

steppercontrolmodulemayaccm.modatea maximumof threesuchmodulesand

thereforethreesteppermotors. Thepulseoutputexpanderis responsiblefor

communicatingthepulseinformationfromthecontrolmoduleto thesteppermotor

itself. In orderto fabricatethesystemshowninFigure7-1, thefollowingpartsmust

be usedfromtheteststationthat iscurrentlysetupinbuilding30:

Table6-1: ControlComponentsfor KWA Ion HandITEM FUNCTION

1771-IBDDCinputmodule providefor localDCinput177I-OBDDCoutputmodule providefor localDCoutput1771-A3B112slotI/Ochassis houseremotel/O modules1771-ASBremoteI/Oadapter providecommunicationforremoterack1771-A2B8 slotI/Ochassis houselocalI/Omodules

4

?naddition,thefollowingcomponentswhicharenotinstockareneeded:

Table6-2: NecessaryControlSystemComponentsfor KIVAIITEM FUNCTION

1771-OBDDC outputmodule ProvideforremoteDCoutputPLC-5/15to 1771ASBtwinaxial Enableconnectionbetweenlocalandcable(either1770-CDor custom remoterack

made) (maximumdistanceis 10,000feet)(tablecontinues)

44

11771-QAstepperpositioning “assembly

Slo-Synsteppermotor

S1o-Syntramlatorlpowersupply(steppermotordrive)

Generatepulsesourcefor steppermotorcontrol

Convertelectricalenergyintousefulmechanicalenergy

Translatedigital informationfrom pulsesource to motor shaft rotation; providepowerandisolation

The remainingitemsnecessaryto realizethe systemshownin Figure6-1 are in stock

on site(i.e.,PC,powersupplies,andconnectors).

6.2 Controlof ACSynchronousConstant SpeedMotors

Whenanapplicationrequireslessdemandingprecisioninsmallmovements,anAC

constantspeedmotorisoftenusedas anonloffdeviceto fulfilltherequirements.For

example,whilea steppermotormightbe usedto preciselypushtwotankstogether

througha leadscrewinoneexperiment,anACconstantspeedmotormightbeusedto

rotatesafetydrums(containingpoison)in andoutby 180°inanotherexperiment.An

ACmotorisdifferentiatedfroma DCmotorby the factthat,for ACmotors,rotor

currentsarenot inducedbya commutatorandbrushes. Instead,currentis inducedin

therotorconductorsby thestator’schangingmagneticfield(sometimesreferredto as

“inductionaction”);thus,thistypeof motoroperatesby settingupa rotatingmagnetic

fieldona rotor.Typically,therotorisof the “squirrelcage”typeandthe rotating

magneticfieldis setupbysendingsinglephasesof muhiphaseACpowerintospecific

“polewindings”(woundupconductivewire).Wheneachphaseof thepolyphaseAC

poweris correctlydirectedto itspolewinding,a magneticfieldis setupwhichtendsto

rotatethesquimelcage. Bycontinuallykeepinga rotatingmagneticfieldappliedin

thisway,thecage(rotor)is keptcontimmllyrotating.Typically,one,two,or three

phaseACpoweris usedto rotatethecage. Thedifferencebetweenthespeedof the

rotatingmagneticfieldandthecageitselfis termedthe“slip.”Whenthedesignof the

45

motorallowsthecageto “lock”intothespeedof therotatingmagneticfield,the “slip”

is zeroandthemotoris saidto be operatingat “synchronousspeed.”Whenthismode

of operationis reached,themotoroperatesat a constantspeedthat isdirectly

proportionalto thefrequencyof thepowersupply.

ACsynchronousconstantspeedmotors,specificallySlo-SynSS seriesmotors,may

becontrolledwithaPLC systemby utilizingtheRCcircuitshowninFigure6-2 [1$].

Figure6-2: AC MotorControlCircuit

Theconstantspeedmotoris turnedon andoffandchangesdirectionby selectingthe

appropriateswitchshowninFigure6-2. Thepurposeof theresistorandcapacitoris

tochangethesinglephaselinevoltageintothetwophasevoltagethat is appropriate

forenergizingthemotorcoils.Althoughan actualthreewayswitchcouldbeusedto

controlthemotorstatus,criticalexperimentsmustbeoperatedremotely;therefore,a

powercontactoutputmodulethatcanopenandcloserelaysmaybe usedto select

fromamongthethreeswitchpositions.Basically,thisty-pcof moduleallowsremote

relaysto be turnedonandoff via thecontrolprogramstwed in themicroprocessor

46

memory(locatedin a localI/Ochassis).Oncethemotorhasreachedits finalposition,

a limitswitchcanbe usedto turnthemotorto itsoff position. In thisway,useof

opticalencoderf=dback iseliminatedwithoutlosingfinalpositionalinformation.

47

Chapter7.

USINGTHE NUMERICALRESULTSTO SIZE HARDWARE

7.1 Introduction

Nowthatthegeneralcontrolsystemcomponentshavebeenestablished,thenext

stepis to sizea motorandtranslatordriveto thespecificjob of runningtheuranyl

nitrateexperiment.Typically,thisinvolvesperfoting thefollowingtasks:

. determinewhattypeof motionisdesired:typicallyeitherlinearor rotational

● approximatethemaximumandminimumallowablevelocitiesbasedon

criticalitycalculationsor measurements

● determinewhattypeof translatorwillbeused

. determinethemotortorquerequired

Thisgeneralprocesshasbeenperformedfortheuranylnitrateslabtankexperiment.

Thegenera!approachis to defineallof therequirementsbasedon thesystem

informationandthenmatchthemanufacturedhardwareto thosespecifications.

7.2HorizontalsolutionAssembly:theSlabTanks

Recallthegeometryandphysicalsetupdiscussedin thepreviouschapters.The

mechanicalgoalis to pushtwocylindricaltankstogetherwithoutaddingmorethan

fivecentsof reactivitypersecond.Thiswillbe achieved,inpart,throughtheuscofa

steppermotorandleadscrewthatwillpushthetablesupportingoneof thetanks

!owardtheotherstationarytank.

7.2.1Requirements

Inorderto preciselychoosethecorrectsteppermotor,it is firstnecessaryto deeide

whatgeneralperformancecharacteristicsmustbesatisfied.Theblocksof information

on thefollowingpageserveas a datasummaryareafora steppermotorthatwillbe

drivinga 61kg massthrougha leadscrew.Notethatcertaincharacteristicsare listed

48

as “tobecalculated.”Thesevalueswillbe determinedlater. Figure7-1showsa

graphicalrepresentationofthedesiredvelocityprofile.

MECHANICALREQUIREMENTS

ApplicationWeight

MountingResolutionAccuracy

Environmental

Damper(to reducesettlingtimeforeachstep)bads orTerminals

Gearing/LeadScrews

Table7-1: MechanicalRequirementsVALUE

TranslationalTableWeight=61 kg

NEMAtypeflange200stepsper revolution(1,80/step)

.0540/step(3%of resolution)Becauseof lowpoweroperation,thereareno special

environmentalconsiderations —

None

8 leadsThompsonleadscrew

Table7-2: LoadRequirementsLOADREQUIREMENTS VALUE

Torqueat speed to be calculatedInertia to becalculated

MaximumSpeed to becalculated

49

(seefigure1)Acceleration/DecelerationRequired .5secto maxvelocity

.5sectostandstillSinglesteptimenxponsedesired 2.5ms

PulseRate Max,Velocity/PulseRate

.5sec Position

Figure7-I: StepperMotorVekbcityI+ofle

7.2.2MaximumSpeedAllowable

Inchapterthree,theabsolutevalueof theslopeof thereactivityvs.airgapplot

wasfoundto beapproximately11.38centshm, whichequals2.89$/inch. The

maximumreactivityinsertionratefora Class11reactor(reactorthatgoesdelayed

critical)asspecifiedbythetechnicalspecificationis fivecentshec.Withthis

information,wemaycalculatethemaximumpermissiblelinearspeedof thesystemas

follows.Thisvaluewillbe usedwhenwritingthecontrolprograminchaptereight.

(maxah~wablereactivity)(constant)maxlinearspeed = —slope

(5=)( 1$ )00 cents=2.89~

inch

= 1.038=

50

Dueto thisextremelyslowspeed,a gearheadreductionwillbe neededinorderto

increasethenominaloperatingspeedofthemom andavoidlowpowerresonance

eff=ts.

7.2.3Basic Formulas

Therearethreebasicformulasthatareoftenusedinchoosingcontrolsystem

componentsfora translationaltypesystemusinga leadscrew. In thecasepresented

here,equation(/) maybeusedtosolveforthegearheadoutputspeed,equation(2)

yieldsthemotorshaftspeed,andequation(3)maybeusedto calculatethepulserate.

G/f = (P)(h”nearSpeetf)[=]qvm (1)

where:

GH=gearheadoutputshaftspeedinrpm

P = leadscrewpitchinthreaddkch

LinearSpeed= speedin incheshinute

Next,thespeedatwhichthemotoris rotatingis foundwith:

AUS= (x)( GH)[=]rpm (2)

where:

MS= motorshaftspeedinrpm

x = theplanetarygearratiox:1

Finally,themaximumpulserateallowablecanbefoundusingtheequation:

PSEC= ~sp:;s)[=$r’::: (3)

51

where:PSEC= pulseskc output by the stepperpositioningassembly

SP= steps/pulse

DS=degreeshtep

7.2,4MaximumPulseRate

Usingthevaluedeterminedforthemaximumspeedallowable,themaximumpulse

rateof thesteppercontrolassemblymaybe calculated

maximumgearheadoutputshaftspeedis foundto be:

GH= IOrpm

Usingequation(1),the

Usingequation(2), themaximummotorspeedis foundto be:

MS= 520rpm

Finally,usingequation(3), themaximumpulseratethatthestepperpositioning

assemblymaysendoutwithoutexceedingthereactivityinsertionlimitis:

PSEC=~60 pUk/H

7.2.5MinimumSpeedPossible

Theabsoluteminimumspeedat whichtheunitcanbe runcanbedeterminedby

consideringthesmallestpulseratethecontroldeviceiscapableofgenerating.

Assumingtheminimumis 1pukkc, useofequations(1) throttgh(3)yielda

minimumspeedof .0025irhin. Sincethispulserateisextremelylowandmight

resultin motorvibrations,a minimumpulsemteof 500pulseskc is assumed.With

thisvalue,theminimumlinearspeedis foundI.Obe .15inhnin.

7.2.6Resolution

Theresolutionmaybe calculatedbyconsideringtheminimumnumberof single

pulsesthestepperassemblycansendout in a onesecondperiod. Thustheresolution

isjust theminimumvelocity(inkc) multipliedbythetotaltimetogeneratethefinite

52

numberof pulses.Fora minimumpulserateof 1pulsehec,theresolution is .00004in.

Fora minimm pulserateof 500pulseshec,theresolutionis .0025in.

7.2.7RequiredOperatingTorque

Thelaststepis tocalculatetheamountof torquerequiredto movethe61kg mass

at thedesiredvelocitybyappiyingthebasicequation:

(4)EM oments= Ia

where:

1= totalsystemmassmomentof inertia

a = angularacceleration

Thetotalsystemmassmomentof inertiais foundbyaddingeachseparateinertia

component:

Itotal = Ieq + IsCrew+ I rotor (5)

Where Ieq istheequivalentinertiaofthemassbeingmoved.TherotorinertiaiSfound

frommanufacture’spublishedMeratursfora selectedsteppermotorto be2.5lb-in2

whilethescrewandequivalentinertiasarefoundwiththe followingequations[18]:

It~(lb- in2) =weightx.025screwpitch

where:

weightis inpounds

screwpitchis in threadsper inch

IK,W(lb- in2)= diameter’x lengthx.028

(6)

(7)

when:

screwdiameterandlengtharebothin inches

.028isthenominaldensityofsteellb/in3

Next,thetotaltorquerequiredis foundusingthefollowingequation:

~O,u,(oz- in)= ~Cc,p,+ T,,iC,iO~

= I,da,x ‘e’*ciV Xconversionfactortime

force+

screwpitchx q x conversionfactors

(8)

where:

velocity[=]rad/sec

time[=]sec

force[=]in/lb

q = screwefficiency

Notethevelocityusedhereis thevelocityin radkx of thegearheadoutputshaft. An

additional10oz-inof torquehasbeenaddedtoaccountformiscellaneoustorques

fromgearheadinertkoroffset loads. AssumingtheconstantsshowninTable7-3,

equations(4) through(8) yielda requiredtorqueof 8.05in-lb.

7.2.8GearheadReduction

Thefinalstepis tochoosethe translator-motor-gearheadcombinationthatwill

satisfj allof therequirementssummarizedabove.Thetotaltorquerequiredto

accelerate!heloadwithouta gearhcadattachedwascalculatedas 8.05in-lb.!Vhenthe

gearheadisadded,it willhavetheeffectof multiplyingthenominalmotortorqueto

increasetheoutputtorque:

O~tputTorque= Motor Torquex Eficiency x Ratio (9)

54

I

Sofora motorwitha ratedtorqueof 1.87in-lbat750rpm,theactualoutputtorque

(k to thegearheadis approximately79.475in-lb(assuminga gearheadefficiencyof

.&f); thisobviouslyexceedstherequiredamountandwouldsufficeforaccelerating

ittt loadto themaximumvelocityin.5 seconds.“Pull-in”torqueis themaximum

to;que thatcan acceleratea loadwithoutlosingsynchronismwiththepulserate. The

‘~.otorchosen musthavea pull-intorquethatis greaterthanthecalculatedvalueof

38.97Oz-in.in additionto providinga torque multiplication,the gearhcadreduction

was used in orderto reducethespeedof thesteppermotorandavoidpossible

vibrationproblemsthat may be present at timlow or high endof thetorquevs.speed

(steps/see)curve. Thetranslatorchosenforthis applicationis theSlo-Syn430-PT

packagedtranslatordrive. Thisdriveoperatesin halfstepmode(0.9 degktep)and

utilizesa bipolarchopper,2 phasesteppermotordrive.

7.3Summary

Allof thecalculationsdiscussedhavebeenplacedin a spreadsheettoexpeditethe

processofparametricvariation.TheresultsareshowninTable7-3on thefollowing

page.Thecalculationsperformedin thissectionhavedefinedthebasicvelocityprofile

andmotortorquetobe usedforthe steppermotorin the uranylnitratesolution

experiment.In.5 seconds,the 17.85inllb(minimum)steppermotorwillacceleratethe

massto a maximumlvelocityof 1.038irthnin.Thiscorrespondsto an accelerationof

17.3rev/sec2to a pulserateof 3461pulsedsec. Withknowledgeof thenumbers

summarizedinTable7-3,alongwiththegeneralprofileshowninFigure7-1,weare

nowin thepositionto programa systemutilizingeitheran integrateddriveor a

separatepuke source.

55

Table7-3: SizingCalcuk#ionsSummary]INPUT PAJ?AMTERS I I 1

12345678

1?31112131415161718

OUTPUT123456789101112131415-161718 TcXdtmuera red(hlb) : 17.85CD7{

Slcpec#rea3ivity@cjt($fin) ~\~ 2.89

Mm. lnsdkn 17’de(omtshw),.Lea3Sc.mwPitch(th/ln) 15 10.Mcx Pdse Rde(pha&x) ~ ~ mm.Plmetay Gea Reckticn f?cilo~ 50.Trcmldx St@ngh&&(st~@se) ~ 0.5.st~ng Ma Resd@cn (ct@t@ : 1.8

.DesircdR~dutkn @n) . O.ml

.Tdd W@@t (M) ! : 4347,Tknetor~vdodty(s ec) ; ~ 0,5.Saavdawta (h) , : ~ 1.5.SmV1.=@h On ).. . ~ . 48.Scxmvf3tch(thjn) . . 5,Screweffidw 0,9.~dg rdcf Inertla(lbin%?) : 2.5:Frldicn facatosli&w@@t(@ ~ 6.Mdrwn PUse Rate,@ sesAmcj . ~.MSC Taw(cx-ln) . . 5FfWAJvE”TE RS,fvb. LimaSpedkwed(ln~n) 11,038062jhkx. G@ i+edOu@t Shcft Spged(rp)! 10.38062~hkx.,Ivk3tcxSpe@(r~) ! I 519.OJ1lNIx Ma Speed(cb@sec) . ] 3114,187.MCX.Pdse Rc#e@ses~@ . . 3~”2~~.Mn. tvkia Speeg(r~),Mn. Ivlda Sp3ed(d3gk) ~ : m,Mn. G&x Hea50ut@ Shd Sp=d(rm). ;.5,Mn. Lima Spf3edQnmn) . .0.15.Mn. Linea Spe@(in&c) ~ o.Qq?5,Eqjvcht hhs InErtia(lblnW): ; 4.-&l7!s~~ IMO fl~jnq) 6:804;Accd=cikm&M~@m (rw,$&2) j i7.3olo4:Totd Inertiaflbjw). I j 30.952g4.Taqmto-qerqfijdt~(~_-in) ~0,21-~. —-...Ta~tocqx@@O syst~ (gzfln) ~280.3891.T@d tgcper-~red(a-in) 285.6011,—. .,

56

Chupter8.

CONTROLSYSTEMPROGRAMMING

8.1Introduction

In thischapter,theinformationgeneratedin theprevioussectionswillbe usedto

writea controlprogramforthetwomainsystems:thehydrauliccircuitandthestepper

motorpackage.The numericalresultsandsizingcalculationsof chapterstwo and

sevenwillbeusedto setthemotorspeedin theprogramandthecontrolsystem

hardwareoutlinedintheotherchapterswillbe“wiredwithsoftware.”Thisisthemain

advantageof a digitalcontrols~tstem:tk systemcharacteristicsmaybequickly

modifiedwithouta greatdealof hardwaxoreffoflinvested;if thecalcu!a!ionsprove

tobeoverlyconservative,thespeedof closuremaybe changedsimplybyre-writinga

fewlinesof code.

Programmingof thePLCcontrolsystemis achievedthroughtheuseof whatis

‘knownas “hidderlogic”prograrnming[2]. Theterm“ladder”refersto the ladderlike

structureof thisgraphicprogramminglanguage(seeprogramlistii~gin AppendixC).

Theprogranum“ngis doneon an IBMcompatiblecomputer,can x savedto thehard

chive,andthenuploadedto theprogrammable logiccontrollerlocatedin the localI/O

chassis;or, theprogrammingcanbedone“on-line”whileconnecteddirectl:~~~the

procewor.Thebasicsignalflowthroughthesystemis shownon thefollowingpagein

Figure8-1[1].

57

InputModuleI I

OutputModuleI I

IntmtDevices:

RocessorMemoryA

Input)

“)

outputData OutputDc~:ices:

switches Data) Table Table > Motors

Joystick LightsSensors Valvesetc.

1+ ~) etc.

Programming(LadderDiagram)

Figure8-1:SignalFlow17voughthe System

Someofthemorebasicladderlogicinstructionsinclude:

● “Examine-on”:if theexaminedbit is “l” the instructionis true

● “Examine-off’:if theexaminedbit is “O”theinstructionis true

● “Blocktransferread/write”:transferblocksof datato or fromartintelligent

module

● “Timeron(TON)flimeroff (TOF)”:timeevents

● “File/Arithmetic/Logical(FAL)”:convert,manipulate,andmovedata

Eachof theseinstructionshasassociatedwithit a mnemonicanda graphicalsymbol

thatis displayedon thescreenwhenusedandwillbediscussedin thischapter.

Theconceptof a examiningandmanipulatingbitsis essentialto understandinghow

a PLCis programmed.Thefactthat inputsandoutputscanhaveonlya valueof “on”

or “off’cangreatlysimplifytheoftendauntingtaskof prograrnrninga seemingly

complexsystem.The “on”(or “high”)settingisdefinedbya pre-determinedvoltage.

If thevoltageonthe lineis greaterthanthatpm-definedvalue,thenthelineis saidto

be “high”;likewise,if thevoltageon thelineis lessthanthepredeterminedvalue,the

statusof the lire is saidto be “low”(orzeroor “off”).Withsuchsimplebinarylogicin

place,onemaythenapplyBooleanalgebrato thestatusof differentlinesby utilizing

simpleintegratedcircuitchipssuchas “nand”gates,“nor”gates,or “exclusiveor”

58

gates(’ITLlogic). Basically,themicroprocessorbasedcontrolsystemoperatesby

assigninga labelto eachbit thatis usedwithinthemicroprocessor.Inthisway,the

status ofeachbitmaybeexamined,managed.andmanipulatedas desiredthroughthe

use of a program.

8.2 Basic ProgrammingConcepts

Figure8-2showsthefundamentalideabehindprogramminga FLC.Basically,the

entireprogramconsistsof a numberof “rungs”inside“steps.”The steps define the

overallprogramflowwhiletherungsdefinethedetailsof theprogram(i.e.,the logic

dictatingwhatwillbe turnedoffandonforexample).Therungshownin Figure8-2

LADDERLOGIC SEQUENTIALFUNCTIONCHART(SFC)(“steps”)

InsideEach“Step”Are“Rungs”2:Q

~ :~’’’’;’’N’’’’’cK)

Figure8-2:BasicPLCfiogrammingConcepts

willexaminethectateot a bit (either“l” or “O”)andthensetan outputbit to “l” if

the examinedbit wasfoundtobe” 1“(i.e.,a truepathresultsinanenergizedoutput).

Thisis the“examineon”iv-truction.

8.3ProgrammingtheAnalogInputModule

Programming theana!oginputmoduleconsistsof initializingthemodulewitha

“blocktransferwrite”(usuallypreconditionedwitha switch).Next,a “blocktransfer

read”mustbedonein ordertocontinuallyreadtheinputfromthemodule(i.e.,the

valueof theanalogsignalcominginas wellas otherstatusbits). Oncethevalueof the

59

analogsignalcomingin isknownandscaiedbytheuserasdesired,theprogrammer

maymanipulate,display,orstorethedatainanywayneeded.Forexample,input

froma potentiometerhooked into a constant voltage DC source couldbe readintothe

inputmodtiie,readbythePLC,andthendisplayedinasevensegmentdisplay.

ADC Rocessor Memory

(AnalogInputModule)AnalogSensor: DataTable

Temperature,Pressure,HowRate,Ctc.

ISteppingMotor, AnalogorDCDeviceValve, metc.

DACor DCoutput

Figure8-3: AnalogInputProgramming

8.4Programmingthe StepperMotorModules

Pmgrammingthesteppermotorassemblyinvolvesinitializingtheassemblywi:ha

blocktransferreadandwrite,andthenprogrammingthedesiredmotionusingthe

ladderlogiclanguage.Thenumlxrandrateof pulsessentbythesteppermotor

assemblydeterminestherateat whichthemotorturns. Pulsesareoutputto themotor

throughtheuseof “moves”in theladderlogicprogramminglanguage.Althoughthis

modulewasnotusedintheprogramwritten,it isplannedtousethis(aswellasan

opticalencodermodule)in thefuture.

8.5Programmingan IntegratedDn”ve

Asdiscussedin chaptersix, theotheralternativeto steppermotorcontrolis an

60

integrateddriveunit. Typicallywithsucha unit,programrningis achievedviaanRS-

232 interfaceas describedinchapterfive. Shownbelowis theprogramthatwas

writtenandstoredinthememoryofthecompumotorAXLdrive.Thisprogramwas

then executed from the ladder logic program stored in the processormodule memory .

LD3MNA17.3V5D2500G

where:

LD3:disablesthe limit switchesMN:setsthe modeto “normal”(i.e.,cansetdistance,acceleration,andvelocity)A17.3: sets the accelerationto 17.3rev/sec2V5:setsthevelocityto 5 rps(max:8.65rpsascalculatedearlier)D2500:setsthedistanceto 2500stepsG:executesthemove

Thisprogramminglanguageis completelyseparatefromthatofthc PLC. As

mentionedbefore,thisisoneincentiveforusinga stepperpositioningassemblyrather

thanan integrateddrive:centralizedprogrammingreducesdocumentationand

complexity.

8.6StepperControlViaan Integratedlk”ve

A programhasbeenwrittenthatsetsthe frameworkforcontrolof theslabtanks

experimentthroughladderlogiccode. Thetwomainsystemscontrolledby the

programarethe hydraulicandsteppermotorsystems(referto Figures1-3and 1-4).

AnintegratedcompumotorAXLdrivewasusedto drivethesteppermotorwhile

lightson the 1O-6OVDCoutputpanelwereusedto symbolizetheon/offactionof

hydrauliccomponents.Byno meansis theprogramshowncomplete.Writingand

puttingtogetherthecontrolsystemfortheentireexperimentwouldi“~wolveadditional

hardwarecomponents,linesof code,andsystems(e.g.,automaticandsecondag

scramsystems).Theprogramdiscussedin thissectionis intendedtoprovidea clear

61

——

exampleof the programmingprocess and methodsand serves as the first version of the

softwarethatwilleventuallycontroltheslabtanksexperiment.

A listingof the AIlen-Bradleyprogram is shown in AppendixC and the following

section gives a rungbyrunginterpretationofthisprogram.Theprogramisdivided

intofiles.Typically,thefilemaybe a ladderlogicfileora sequentialfunctionchart

file.A sequentialfunctionchartis the“overall”pictureof the programand contains

steps, shownasrectangleson the listing. Withineachstepis a ladderlogicprogram.

Thisisdirectlyanalogousto theconceptof modularprogrammingin FORTRANwith

subroutines.TheflowwithintheSFCiscontrolledby “transition”ladderlogicfiles

whichdictatewhetheror notcontinuitywillbegrantedso thattheparticularstepmay

be run.Transitionsoperatelikeon/offvalvesregulatingwhichiadderlogicprograms

willbe scannedby theprocessor.Theseconceptsareclarifiedgreatlybywalking

througheachsectionof theprogramshownin AppendixC (thenextsection).

Asprogrammed,thebasicoperationof thecriticalassemblyis as follows(referto

theSFCin AppendixC). Afterthe initializationandclearstepsareautomatically

completed,theuserhastwomodesto selectfromviatoggleswitches:eitherrunor

test. In runmode,theuseris forcedto firstclosetheair gapwiththehydraulic

cylinder.Onceclosureviathecylinderhasreacheda pre-&finedlimit,theusermay

thenclosetheairgapvia thesteppermotor. Throughouttheapproachto critical,the

userhastheoptionof scrammingthemachineusingthescrambutton. Oncethe

minimumpossibleairgapisreached,boththehydrauliccylinderandthesteppermotor

arede-activated(to preventa runawaychainreaction,an automaticscramsystemis

usuallybuiltintothesystemas well). Intestmode,thesteppermotorandhydraulic

ram arebothde-energizedinorderto providefor testingof thevalves. ThevaJves

maybe forcedon andoffby forcingbitson or off fromthecontrolprogram.

62

8.7 SequentialFunctionChart:File001

Theactualsequentialfunctionchart(SFC)isshowninAppendixCandit is

illustratedfor clarity in Figure 8-4. A total of 12files were created (Table 8-1).

FileNumber

001

002

003

004

007

008

009

10

11

12

Table8-1: !

Name

MAIN

30YSTICK

INIT_DONE

INIT

CLE.4R

RUN

TESTS

DONE

CONTROLS

MAINTAIN

NOPS

h TankProgramFiles

Function—.-

Scquentialfunctionchartfile— ---

Coni”dtheDCoutputsviaswitchesand

thepotentiometer.Thisis fundamentally

thesameas ajoystickcontroldevice.

Controlthe transitionfromfile004

(INIT)to file006(CLEAR)

Initializehardware

Ensurethatall outputsareoff before

continuing

Selectthemn branchto runthemachine

Selectthetestbranchto testthemachine

Controlthetransitionfromtestingor

nmningto thefinish

Controlthesteppermotorandhydraulic

system

Testthehydraulicvalveswiththemotor

andpumpoff

Emptytransition

63

Files5, 13,and14shownontheprogramlistingremainedemptyandwereneverused.

64

startvINIT

~ANS ITION:INIT.00NE

CLEAR

TRANSITIOhTESTSANSITION:RUN

COPJ’IROLSJOYSTICK

TRANSITIONDONEu + TRANSITION: DONE

I

9CLEAR

TRANSITION:NOPS

End

Figure8-4: GeneralFeaturesof the SFC

Programflowforthesequentialfunctionchartis fromtop to bottom. Whentwo files

(“steps”)areplacedin parallellikefiles002and 10(CONTROUANDJOYSTICK),

theyarescanned(i.e.,run)simultaneouslyby theprocessor.Whena transitionlike

INIT-DONE(file003)goestrue,it allowstheprocessorto dropdownandbranchto

eitherof twooptionmodes:runor test. Whentherunmodeis selected,JOYSTICK

(002)andCONTROLS(10)arebothsimultaneouslyscanned by theprocessor

allowingtheusertooperatetheassemblyforanexperiment.Whenthe testmodeis

selected,theassemblyisdeactivatedto allowfortestingof thehydraulicvalves. Once

eithertestor runhasbeencompletedandthemachineis scramme~theprocessorruns

throughtheCLEARstepthatensurestheassemblyisoff andthenreturnsprogram

controlto fileINITat thetopof thesequentialfbnctionchatt.

8.8 Ludder LQgic:Files 002-12

Arungisspecifiedbythefilethatit is in,andtherungnumber.So,forexample,in

AppendixCat thebeginningof theladderlisting,“Rung2:0”indicatesthatwithinfile

002(denotedby the“2”), thisis the firstrung(denotedby “O”).Whenthepathon a

rungis true,it proceedsto theinstructionfurthestrightandexecutesit. The

instructionsfoundon therightarereferredto as outputinstructionsandareusedto “

turnonmotors,lights,or anyotherdevicethatmustbecontrolled.Theprocessor

scanstherungsfromleft to rightandtopto bottom.

8.8.1Rung2:0

Thisis the firstnmgin file2 “JOYSTICK.”Thefirsttwoinstructionson thisrung

examinetwodifferentbits fortheirstatus. If thebitsarefoundto be “O”in thedata

table,thenthepathis tree;othenvise,ifbet!!bitsare”l,” thenthepathis false(this is

the“examineoff’ instructiondiscussedearlier).Thebitsexaminedare“enable”bits

thattelltheprogramwhetheror nottheanaloginputmodulecanbe read. Whenthe

pathis true,the “BTR”(BlockTransferRead)instructionis executed.This

instmctionreadsthepowerstatusof theanaloginputmodule.

8.8.2Rung2:1

This rungbasicallysays:“iftheBTW(BlockTransferWrite)is notalreadydone,

thendo it”by examiningtheBTWdonebit. WhentheBTWwriteinstructionis

executed,it writesa configurationfileto theanaloginputmodule.Thisconfiguration

filedeterminesthingslikewhatkindof analoginputwillbe used,howtheanaloginput

willbe scaled,orwhethertheinputwillbedigitallyfiltered.

8.8.3Rung2:2

Thisrungcheckstheanaloginputvaluefromthevariablevoltagesourceandsets

bitslocatedin a binarydatatabledependingon thevalue. A literalinterpretationof

65

this rungisas follows:if thejoystickvalueisgreaterthan5(KNand less than9619 and

if the steppermotoris offand ifswitch1isonand ifpushbutton1ispushed,thenset

the “pump”bit to 1.This bit is examinedin theCONTROLSsteptodetermine

whetherthepumpshouldbe energizedor not.

8.8.4Rung2:3

Thisis the same logic used in rung 2:2 with the exception that the “stepmotor”bit

isbeingsetinsteadofthe“pump”bit. ThisbitisexaminedintheCONTROLSstepto

determinewhetherthesteppermotorshouldbeenergized.

8.8.5Rung3:0

Thisis thetransitionfileMT-DONE usedto verifythatproperinitializationhas

occurredin the INITstep.Thetransitionbecomestrueonce the INI’’I-DONEbit is

set true in the initializationroutine.

8.8.6 Rungs4:0

This is the initializationstep,the firstblockexecutedby theprocessor.Typically,a

numberof I/Odevicesrequiresomeformof initializationbeforebeingused. Although

nosuchdeviceswereusedas prutof thisexample,thisstepwasincludedsincesuch

blocksaresocommonwhenwritinga lengthycontrolprogram.Theexternallights

locatedon theDCoutputmodulewerereservedto representinitializationoutputs.

Whenswitchoneis turnedon,rung4:0 startsa ten secondtimer. Whenthe timer

reachesone,two,three,and foursecondsrespectively,lights10,11,12,and 13are

‘“latched”on. A latch commandretentivelysetstheoutputstatehigh;thatis, when

power is lost,theoutputwillremainin a highstate.

8.8.7Rung4:i’

Thisrungturnsoff (“unlatches”)lights10-13if switch1is turnedoff. An

“unlatch”commandretentivelysetstheoutputdevice’sstatusto “O.”

66

8.8.8 Rung4:2

Thisrungchecksthevalueof thetimer. Whenthevaluereaches5 seconds,lights

10-13are turnedoff.

8.8.9Rung4:3

Thisrungturnsallof theinitializationligh!sbackonwhenthetimerreaches6 seconds.

8.R1ORungs4:4 - 4:8

Rung4:4performsanFALinstruction(“FileArithmetic/Logical”)whenthetimer

value reaches7 seconds. The FALinstructionallowstheuserto sendanyword(16

bits)to anoutputlocation. In thisexample,a random16bit sequenceis sentto the

DCoutputmoduleto flashthelightsina randomsequenceto furtheisimulate

initializinga module. Thisinstructionmaybeusedtoarithmeticallymanipulate,

convert,move,andperformBooleanlogicto individualbits orcodednumericaldata.

Rungs4:54:8 utilizetheFALinstructionina similarmannerto flashandblankthe

initializationlights.

8.8.11Rungs4:9 -4:10

Thisrungresetstimersthatareusedin theCONTROLSstepandlatchesthe

INIT-DONEbit inorderto recordin thedatatablethat initializationhcsbeen

completed.

8.8.12Rung6:0

ThisrungensuresthatthePUMPandSTEPMOTORbits in thedatatableare

unlatchedandalsounlatchestheNT-DONE bit incasetheusergoesthroughthe

SFCmorethanonce.

8.8.13Rung 7:0

if therunselectionswitchis onand if thetestselectionswitchisoff, thenthis

transitionrungbecomestrueandrunmodehasbeenselected.

67

I

8.8.14Rung8:0

If the tsst selectionswitchis onmd if therunselectionswitchis off, thenthis

transitionrungbecomestrueandtestmodehasbeenselected.

8.8.15 Rung9:0

Ift!!epumpand stepperand N.O. valve and N.C.l valve and N.C.2 valve am off

and if thescrambuttonis on, thenthistransitionis true,andcontrolis returnedto file

004(INIT).

8.8.16Rung 10:0

If the pumpbit is true,thenstarta 5 secondretentivetimer,energizethepump,and

opentheN.C.I valve.Alongwithrung 10:1,thispressurizesthecylinderandbegins

movingthetankstogetherviathehydraulicram. Theretentivetimerretainsthe

accumulatedtimethepumphasbeenrun(eventhoughtherungmaygo false)as a

meansof ~eterminingwhenthepumpshouldbeabandonedin favorof the increased

resolutionofferedby thesteppermotor.

8.8.17Rung 10:1

If PB2 is off,and if thescramlatchbit isoffand if the run selectionswitchis on,

thenenergizetheN.O.valve(thusclosingit andpreventinga scram)andde-energize

theN.C.2 valve(thusselectingtheclosurespeedsetby theN.C. 1valve).

8.8.18Rung 10:2

If thesteppermotoris on, thenstarta tensecondretentivetimerandenergizethe

steppermotorforoperation.Thetimeris usedinconjunctionwithlimitswitchesto

determinewhenallclosureshouldbeterminated.Knowingthelinearvelocityof the

table(calculatedinchaptereightas 1.03inhnin)andgiventhemaximumdistancethe

tankmaybe movedviathestepper,thenthemaximumamountof timethesteppermay

beoperatedis knownandmaybe set in thetimer.Thisinformationmaybe usedas a

68

redundancytothelimitswitcheswhichphysicallysensewhenacettainpositionhm

been reached.The same idea applies to the hydraulictimer mentionedearlier.

8.8.19 Rung10:3

If thepumptimeris done(i.e.,fivesecondshavebeenreached)or if thelimit

switchforthehydraulicramhasbeenactivated,thenturnoff thepump,unlatchthe

pumpbit,andclosetheN.C.1valve(thushaltingmovementof theslabtankvia the

hydraulicram).

8.8.20Rung10:4

If the steppertimeris done(i.e., ten seconds has been reached) or if the stepper

limit switchhasbeenactivatm thenunlatchthesteppermotorbit andturnoff the

steppermotor(thushaltingallmovementviaboththehydraulicramandthestepper

motor).

8.8.21Rung10:5

If the scrambuttonis pressed,thenopentheN.O.valve,closetheN.C.1andN.C.

2 valves,latchthescramlatchbit, andturnoff thesteppermotor.Thispressurizesthe

cylindercaus!ngit to quicklymovethetanksapartandensuringnoclosureviathe

steppermotor.

8.8.22Rung11:0

If the testseltztionswitchis on, thenturnoff thepumpandsteppermotor.Thisis

themaintenancemodethatallowsfortestingof thevalveswithoutthepumpor

steppermotoron.

8.8.23Rung11:1

Thisrungisexactlythesameas rung 10:5interpretedabovewiththeexception

thatit isplacedin theMAINTAINstep.

69

8.9 Summary

Thisprogramwaswrittenwiththemajorgoalof illustratingthebasicsof

prograrnrm“nga typicalPLC.Theanaloginputsimulatesajoystickand theDCI/O

areusedto controlvalves,motors,or anyotherdevicerequiring1O-6OVDCvoltage.

Whenwritingtheprogramto controlanysystemusingthistypeof PLC,the

commandsandstructuresshownwillbe usedrepeatedly;therefore,theprogram

discussedis a representativesampleofmuchlarger,butnomoreconceptuallydifficult,

controlprogram.Theprogramshownin AppendixC isversiononeof theuranyl

nitrateslabtankexperimentcontrolprogram.

70

Chupter9.

USERINTERFACESOFTWARE

9.1 Overview

Oncethemicroprocessorcontrolprogramhasbeenwrittenanddebuggedandthe

hardwareestablished,theuserinterfacemustbedefinedandcreated. Ideally,theuser

wouldinterfacewitha graphicalrepresentationof thephysicalsystembeingcontrolled

aswellas a controlpanelconsistingof switches,buttons,ajoystick,andanyother

similarinputdevicesthatmightbenecessary.Asin theselectionof thecontrolsystem

hardware,therearetwooptionsthatmaybe pursuedwhenconsideringhowtheuser

willinteractwiththecontrolsystem. If thecustomapproachis beingfollowed,one

mustwritetheinterfacesoftware“fromscratch”usingprogramminglanguagessuchas

C or BASIC. Ontheotherhand,if a systemhasbeenpurchased,a softwarepackage

is typicailyavailableto augmentthehardwareandserveas a linkbetweentheuser,the

controlprogram,and the actualhardware.In thecaseof thesystemthatwas

purchasedandoutlinedin thepreviouschapters,a softwarepackagecalled

ControlViewwasavailable.

9.2GeneralFeatures

ControlViewoffersa widevarietyof capabilitiesthatinvolvea relativelysmall

amountof labor. Thesoftwareallowstheuserto “tag”memorylocationsin thePLC

anddisplaythevalueson thescreenin a graphicalor numericalmanner;it “talks”to

thePLCviathe 1784KT/Bcommunicationscardshownin Figure5-3. Oncethe

memorylocationsof interesthavebeentagged,a databaseof thecurrentvaluesis

createdandcontinuallyupdatedas thesoftwarescanstheprocessorfor thevalues

locatedineachof thetaggedmemorypositions.Afterthisdatabaseis created,the

usermayproceedto thegraphicseditor;here,a graphicairepresentationof the

-7!

physicalprocessbeingcontrolledmayheciGakd.I’heusermaydisplaythenumerical

valueof taggedmemory,drawgeometricshapes,andevenanimateor fillsuchshapes

at a rateproportionalto a value in memory. For example, if the positionof the

hydraulicramis fedbackas an analogvalueviaanopticalencoder,thena rectangular

figurecanbedrawnon theinterfacescreenthatwillfillwitha color proportionalto

thepositionof the ram. Whentheramisat its“out”position,therectanglewillbe

empty of color; when the ram is at its full “in”position, the rectangle will be

completelyfilledwkhthecolorchosen.Suchaninterfacewascreatedfor theuranyl

nitrateexperimentandisdiscussedin the followingsection. In additionto such

features, the softwareprovidesothercapabilitiessuchaseventdetection,alarming,

mathematicalmanipulationof data,menucreation,andsecurityadministration.

9.3UranylNitrateExperimentInterfxce

Aninterfacefor theprogramandhardwarsdevelopedfortheuranylnitrate

experimentwascreatedusingtheControlViewsoftware.Basically,Figures 1-3and 1-

4 were taken, reproduced into one display using the graphicseditor available,and then

linked to memorylocationsdefinedin the ladderprogramlistedinAppendixC. The

steppermotorandhydraulicramaredrawnas rectanglesof differentsizesthat fill

greenwhenfullyextended.Thenormallyopenandnormallyclosedvalvesas wellas

thepumpin the programareshownas redwhenclosed(oroff)andgreenwhenopen

(oron). Theswitchesandpushbuttonscontrollingtheseactionsarewiredas shown

inFigure 5-3 and placed inside a small aluminumbox servingas thecontrolpanel.

Theseswitchesaredisplayedon thecontrolscreenas rectangularbuttonsthatturn

greenwhenon andredwhenoff.Whenthehydraulicramis actuated,theentirecart is

animatedandmovesforwardtowardsthe fixedslabtankwhiletherectangle

representingtheramis filledgreen. Oncethemaximumdisplacementviatheramis

72

realized, it is deactivatedand the stepper motor is selected. When the stepper motor is

activated, therectanglerepresentingthe stepper motor begins to fill with green and the

movableslab tank continues its approach towardthe fixed tank. When the system is

scrammed,thecart is returnedto itsoriginalpositionandtheairgapbetweenthe

tanksis increasedto its maximumvalue. Figure9-2 on the followingpage shows a

screenshotof theinterfacethatwascreated.

Thecreationof theuserinterfacecompletestheprogrammingexamplethatwas

begunin thepreviouschapter. It is worthnotingthattheinterfaceisjust that:an

interface.Althoughit readsvaluesfromthePLC,it innowaycontrolsthephysical

system.Theonlysoftwarecapableof energizingoutputbits is theladderlogic

programdiscussedin thepreviouschapter. Again,althoughthe interface,ladder

program,and hardwarethat have been discusseddo not fully satisfyeach and every

requirementnecessaryforperformingtheuranylnitrateexperiment,theirdevelopment

asoutlinedherelaysthepreliminarygroundworkthatiscrucialtocreatingthemuch

larger,butnomoreconceptuallydifficultfinalsystem.

73

II--mm

OFF

I

Ii!l RUNu I

1

EEKl

74

Figure9-1: ScreenShotof ComputerGeneratedInt@&e

chapter10.

COSTESTIMATE10.1LaborCosts

It isestimatedthattwofull-timeengineerswillbeneededinordertoimplementthe

experimentoutlinedinthisdocument.Oneengineerwillberesponsiblefor

implementationof thecontrolsystemandhardwaremanufacturingwhjletheother

enginee:.willbe responsibleforthenuclearengineeringconcerns;it is assumedthat

bothWNworkonexperimentdocumentation.Assumingappro~.imatelythreemonths

of worktime,theengineeringcostis calculatedas:

(50$#w)x (8hr/&y)x (90hys)x (2)= $72,000 (10)

It is anticipatedthattwotechnicians(onemechanical,oneelectrical)willbe needed

tocompletetheexperiment.Inaddition,onedraftsmanwillbe needed The

mechanicaltechnicianwillbe responsibleforfabricatingpartsin theshopwhilethe

electricaltechnicianwillberesponsibleforwiringthecontrolsystem;theddtsman

willbe responsiblefordocumentingelectricalandmechanicalconstmc!ion.Assuming

threemonthsof work,techniciancostjs calculatedas:

(30$/hr)x (8hrAiay)x (90dizys)x (3)= $64,800

10.2Material Costs

Thehardwareneededfor theexperimentmaybe brokenup intotwoareas:the

mechanicalhardwareandthecontrolsystemhardware.

10.2.1MechanicalHardware

Themechanicalhardwarecostsareestimatedwiththeassumptionthathardware

willbemanufacturedanddesigned“h house.”Table10-1summarizesthegeneral

anticipatedhardwarecosts.

(11)

75

a Wu, v a w-a ● np~ w W* W,SWSG ● aut W WWJ S Vuoms

ITEM APPROXIMATE

COST

Materialfor twotranslationstages(SST) $100

Micrometerhead $100

Stepper Motor $120

AluminumMaterial $100

Miscellaneoushardware(fasteners,welding $]00

materials,etc.)

APPROXIMATETOTAL HARDWARE $520

COST

10.2.2ControlSystemHardware

Table10-2: ApproximateControlHardwareCosts

ITEM APPROXIMATECOST

2 DCOutputModules $600

ElectricalCabling $100

Stepper Positioning.Modules $2,080

Translator $800

APPROXIMATETOTALCONTROL $3,580

[ HARDWARECOST I 1

76

10.3 CostSummary

Summingtogetherthelaborandmaterialcostsandadding10%forunfweseen

contingencies,thetotalestimatedcostfor the experiment is shownbelow in

Table10-3.

T~lble10-3: To&lEstimatedCost

ITEM VALUE

Materials $4,100

14a~ I $136,800

TOTAL DIRECTCOST $140,900

10%Contingencies $14,090

TOTAL ESTIMATEDCOST $154,990

77

78

Chapter11.

CONCLUSIONS

This thesis has addressed the problemof setting up and programminga

microprocessorbaseddigitalcontrolsystem(PLC)forcontrollingacriticalexperiment

involvinghighlyenricheduranylnitrateincylindricalgeometry. Asa resuhof this

study,wemaydrawthe followingconclusions:

● AnAllen-Bradleymicroprocessor-baseddigitalcontrolsystemis theidealchoice

forcriticalexperimentcontrolbecauseof its tlexibility,relativesimplicity,and

proventrackrecord. Implementingthistypeof controlsystemforcritical

experimentcontrolis highlydesirablesinceit providesa commonplatfoxmfrom

whichtocontrola varietyof criticalexperiments.Thisisgenerallynotthecasefor

systemscustomizedtospecificexperimentssincetheresultis a patchworkof

differentcontrolsystems,eachwithitsownuniqueapproachtocontrol. An

Allen-BradleyPLCunifiestheapproachtocontrolwhilemaintainingtheflexibility

to performmanydifferentexperiments.

. Themechanicaldesignrequirementsforperforminga criticalexperimentwith

cylindricalgeometryon a horizontaltableareachievable.Theserequirements

includethedesignof spaceframesto holdtheslabtanks,aswellas a translation

tableforpositioningthemovabletank. Inaddition,therearedistinctsafety

advantagesinperformingsuchanexperimenthorizontallyratherthanvertically

includingthepossibilityof a gravityassistedscrammechanismandeliminationof

theworstcasescenarioinwhichonetankdropsverticallyontotheother.

. A probabilisticcomputercodesuchas MCNPmaybe usedforsensitivitystudies

to providea roughestimateof systemsensitivity;however,dueto thestatistical

natureof sucha code,it is notideallysuitedto sensitivitystudiesrequiringa high

degreeof accuracy.Wemayconcludethatthecylindricaluranylnitratesystem

discussedisvetysensitivetochangesintheairgap:approximately9centshnmto

14centshm.

. Theresolutionrequiredfortheuranylnitrateexperimentis achievableusinga

steppermotor,leadscrew,andgearheadreductionforfineadjustment.

In general.thisstudyhasproventhata PLC system manufacturedby the Allen- ‘

Bradleycorporationoffers the flexibilityneededto performnot only the uranyl nitrate

experiment,but a widevarietyofcriticalexperimentsinvolvingfissilematerial.A

unifiedapproachtocriticalexperimentcontrolhasbeenpresentedthat,when

implemented,willgreatlyenhancethecapabilityofthc LosA1arnosCritical

ExperimentsFacilitytosafelyandexpeditiouslygathervaluablecriticalitydataviaa

commoncontrolsystem.

79

REFERENCES

[1] AllenBradleyCompany. 1992.Introductionto Programminga 1785-PLC-5ProgrammableController,Student’sManual. Wisconsin:AllenBradleyCompany.

[2] AlienBradleyCompany. 1992 PLC-5ProgrammingSo@are Manuals.Wisconsin:AllenBradleyCompny.

[3] Allen-BradleyCompany.1991.PLC-5and ModuleinstallationManuals.Wisconsin:AllenBradleyCompany.

[4] Anderson,R. 1986. PersonalNotesfora SolutionArrayExperiment. LosAlamosNationalLaboratory:GroupN-2.

[5] Bociine,Clay. 1978. till Motor&Geannoto& Cent o! HandbookrFourthUULQL

. . IllinoixRodineElectricCompany.

[6] Briesmeister,J. et al. 1986.A4CNP-AGeneralMonte CarloCodejorNeutronand PhotonTransport. Los AlamosNationalLaboratory:ManuaiLA-7396-MRev. 2.

[7] CompumotorDivision,PnikerHannifinCorporation.1989.AXDrive Users’Guide. California:CompumotorDivision.

[8] Houpis,C.; Lament,G. 1992.Q@”talControlSvs!ems7%off. Hae r~w~. .

$oilware. SecondE$ulon%New York:McGraw-Hill.

[9] Lamarsh,John. 1983. lhtroduan to Nuc&QrEw?mee n~. . .ri

Massachusetts:Addison-WesleyI%b!ishingComp’any.

[10] Osbom,L.et al. 1970. HydraulicSystemfor HoneycombCart. Los AlamosNationalLaboratory:Drawing19Y-29431C38.

[11] Patemostcr,R.R.et al. 1992. SafetyAnalysisReport~orPajarito Site(TA-J8)and the LosAlamos CriticalExperimentsFacility (LACEF). Los AkimosNationalLaboratory:ReportLA-CP-92-235.

[12] Paxton.HughC. 1983.A Histoq~ofCritical Experimentsat Pajarito Site.Los AlamosNationalLaboratory:ReportLA-9685-H.

80

[13]

[14]

115]

[16]

[17]

[18]

[19]

petm’~l!a. Frank D. 1989, ~~ ~ontrol~”r.~ New York:McGraw-Hill.

Sanchez, Rene. 1993. PersonalNotes ONNuclearEngineeringFundamentok Los AlamosNationalLa*oratory:GroupN-2

Schlesser,JohnA.et id. 1992.Nuclear CriticalitySafety:3-Day TrainingCourse,SfudenrsManual. Los AlamoiNationall,abora!ory:ManualLA-12387-M.

Siege!,Robert;Howell,John. 1992.~. on ~~“ ii ~~h WtihiflgtoriD.C.:HernisphcrePt~blishi~gCorporation.

Spriggs,GreggD.et al. 1986. Cri~icalityof Uranyl-NitrateSolutionin SlubGeonletry. Los AlamosNationalLaboratory:ReportLA-UR-06-2245.

SuperiorElectricCompany. 1975.DesignEngineersGuide to IICSteppingMotorsandAC SynchrmousMotors. Connecticut:SuperiorElectricCompany.

Vande Vegte,John. 1990.~~v~~ Ew~NewJersey:PrenticeHail.

81

AppendtiA

MCNPCardSummary

Surface Cards

The surfacecards define generic surfacessuch as cylinders,spheres,planes, or

ellipsoids. Surfacecards are referencedby a surfacecard number. For example, in

order to define an infinitecylinderalongthe y axis,one wouldenter the followingline

in !he input file:

1 Cy 36.195

This card says “surface 1is definedby an infinitecylinderalongthe y axis with a radius

of 36.195cm.” Similarsurfacecard mnemonicsmaybe used to define spheres, infinite

planes,and other standardgeometricalshapes whoseequationsare well defined by

analyticgeometry.

Cell Cards

The geometryof the system is specifiedby applyingBooleanoperators to the

surfacecards. For example,surfacecard 1 may specifya cylinder(infinitein length)

alongthe Y axis and surfacecards 2 and 3 may specify two infiniteplanes

perpendicu~arto that cylinder (planes 1 and 2 ). In order to define a systemconsisting

of a cylinder with finiteends (referredto as a “cell”),one may insert the following

geometrycard in the input file:

1 10 -7.9 2 -3-1

Thiscardsays“cell1isdefinedbyeverythingto thepositivesense(totheright)of

surface2 intersectedwith everything to the negativesense (to the left) of surface 3

intersectedwith everythingto the negativesense (inside)surface 1“(italicnumbers).

The numbersthat aren’tin italic type representthe material type (10, in reference to

materialcard 10)and the materialdensity (7.9) in grardcc.

85

VarianceRedl . ‘on:ImportanceCards

Importancecards are the most common form of variance reductionavailable to the

MCNP user. With this card, the “importance”of each cell maybe assigneda value of

one (important)or zero (not important). If a cell is assigned an importanceof zero,

particlesenteringthat cell wili not be followedor banked as part of the “game.” Cells

that ~re “voids”(contain no material ) and that are predicted to have little or no

influenceon the system understudy are typicallyassignedan importanceof zero in

order to reduce computer time.

MateriulCards

Materialspecificationcards do just what their name implies: ICllthe ccmputer what

kind of mat.rial the cell is composedof. This informationis typicallytransmittedin

the form of numberdensities (atoms/bam-cm)and cross section table references.

Materialspecificationcards fix the relativeproportionof each element or nuclide

withineach cell and dictate whichcross section tables will be used (the probability

portion of the “game”being played). MCNP really cares only about the relative

proportionof each element or nuclide within the material;therefore,either number

densitiesor atom fractionscan be entered in the materialcard since atom fractionsare

foundsimplyby multiplyingthe numberdensitiesby a constant. Also as a resultof

this, the numberdensitiesof a certain materialcan be summedand the resultingvalue

may be entered as the densityon thecell card. Thisis indicatedbyenteringthevalue

withouta negativesignprecedingit (seeinputfiles,AppendixD).

86

Mode and Tally Cards

Lastly,MCNP mode and tally cards are used to determine the operation mode of

MCNP and the data that is to be tabulated as the simulationis being run. When doing

criticalitycalculations,the “kcode”card is alwaysused. This card allows for the

definitionof the position, and size of neutronsources that are present as well as a few

other parametersrelated to programexecution. The tally cams determine what data

will be generatedby the program.Options(amongmany others) includeneutron flux,

current, and fluence. For this study, the main parameterof interestwas keff:a

parameterthat is automaticallycalculatedfor the user when doing kcode calculations.

ComputerCharacteristics

A total of six input files werecreated.These files were accessedby MCNP version3A

on a Sun Spare 10workstationwith 32 megabytesof memory and a 40 MHZclock

speed. The operating system used was Solaris 1.0.1.

87

Appendix B

Number Density Calcuhztions

A

[ ~

b y

Rcc ~ P]= ~

x

=

()* X I

=

( .)~ X ) X )

()~.

= +

=

0 ) =

[

3

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=

s u t

=

+ =

= +

=

X X )

=

= =

=

T

= - -

= 1 .

=

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=

= =

=

=

= =

=

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= = +

=

=

C

..

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+ *

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.

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106

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107

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128